Label gets blank on updating Listview

Hi,
I am using listview in xamarin forms.

It has the viewcell function like this

public class VetCell : ViewCell
{
public ViewCellModel ViewCell;
public Label SerialNum = new Label();
public Label PLUNumber = new Label();
public Label PLUDescription = new Label();
public Label Price = new Label();
public Image menuImage = new Image();
public Grid ViewCellGrid;
public Grid LastGrid;
public Label SerialNum4 = new Label();
public Label SerialNum5 = new Label();
public Label SerialNum6 = new Label();
public Frame FrameLayout = new Frame();

    public VetCell():base()
    {
        ViewCell = new ViewCellModel() { Color1=Color.Pink };
        BindingContext = ViewCell;
        var nameLayout = CreateCellLayout();

        var viewLayout = new StackLayout()
        {
            Orientation = StackOrientation.Horizontal,
            Children = { nameLayout }
        };
        viewLayout.SetBinding(Layout.BackgroundColorProperty, new Binding("Color"));
        View = viewLayout;
    }


    StackLayout CreateCellLayout()
    {
        ViewCellGrid = new Grid();

        ViewCellGrid.RowDefinitions = new RowDefinitionCollection();
        ViewCellGrid.ColumnDefinitions = new ColumnDefinitionCollection();

        ViewCellGrid.RowDefinitions.Add(new RowDefinition { Height=new GridLength(1,GridUnitType.Star) });

        ViewCellGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });
        ViewCellGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(2, GridUnitType.Star) });
        ViewCellGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(5, GridUnitType.Star) });
        ViewCellGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(2, GridUnitType.Star) });
        ViewCellGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(2, GridUnitType.Star) });

        ViewCellGrid.Padding = new Thickness(1);
        ViewCellGrid.RowSpacing = 0.5;
        ViewCellGrid.ColumnSpacing = 0.5;
        ViewCellGrid.HorizontalOptions = LayoutOptions.FillAndExpand;

        SerialNum = new Label
        {

            FontSize = 25,
            FontAttributes = FontAttributes.None,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            BackgroundColor=Color.White,
            TextColor=Color.Gray,
            XAlign=TextAlignment.Center

        };
        SerialNum.SetBinding(Label.TextProperty, new Binding("SerialNo"));

        PLUNumber = new Label
        {

            FontSize = 25,
            FontAttributes = FontAttributes.None,
            BackgroundColor = Color.White,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            TextColor = Color.Black,
            XAlign = TextAlignment.Center
        };
        PLUNumber.SetBinding(Label.TextProperty, new Binding("PLUNumber"));

        PLUDescription = new Label
        {

            FontSize = 25,
            FontAttributes = FontAttributes.None,
            BackgroundColor = Color.White,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            TextColor = Color.Black,
            XAlign = TextAlignment.Center
        };
        PLUDescription.SetBinding(Label.TextProperty, new Binding("PLUDescription"));

        Price = new Label
        {

            FontSize = 25,
            FontAttributes = FontAttributes.None,
            BackgroundColor = Color.White,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            TextColor = Color.Black,
            XAlign = TextAlignment.Center
        };
        Price.SetBinding(Label.TextProperty, new Binding("Price"));

        LastGrid = new Grid();
        LastGrid.HorizontalOptions = LayoutOptions.FillAndExpand;
        LastGrid.BackgroundColor = Color.FromHex("#e6e6e6");

        //LastGrid.SetBinding(Grid.BackgroundColorProperty, new Binding("Color"));

        LastGrid.RowDefinitions = new RowDefinitionCollection();
        LastGrid.ColumnDefinitions = new ColumnDefinitionCollection();


        LastGrid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        LastGrid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });
        LastGrid.RowDefinitions.Add(new RowDefinition { Height = new GridLength(1, GridUnitType.Star) });

        LastGrid.ColumnDefinitions.Add(new ColumnDefinition { Width = new GridLength(1, GridUnitType.Star) });

        SerialNum4 = new Label
        {
            Text = "$",
            TextColor = Color.Black,
            HorizontalOptions =LayoutOptions.FillAndExpand,
            BackgroundColor=Color.Pink,
            XAlign = TextAlignment.Center,
            YAlign = TextAlignment.Center
        };
       // SerialNum4.SetBinding(Label.BackgroundColorProperty,new Binding("Color"));

        SerialNum5 = new Label
        {
            Text = "%",
            TextColor = Color.Black,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            XAlign = TextAlignment.Center,
            YAlign = TextAlignment.Center
        };
        //SerialNum5.BackgroundColor = Color.Pink;
       SerialNum5.SetBinding(Label.BackgroundColorProperty, new Binding("Color, Converter ={ StaticResource LabelBackGroundConverter }"));

        SerialNum6 = new Label
        {
            Text = "New",
            TextColor = Color.Black,
            HorizontalOptions = LayoutOptions.FillAndExpand,
            BackgroundColor = Color.Pink,
            XAlign = TextAlignment.Center,
            YAlign = TextAlignment.Center
        };
       // SerialNum6.SetBinding(Label.BackgroundColorProperty, new Binding("Color"));

        LastGrid.Children.Add(SerialNum4, 0, 0);
        LastGrid.Children.Add(SerialNum5, 0, 1);
        LastGrid.Children.Add(SerialNum6, 0, 2);

        ViewCellGrid.Children.Add(SerialNum, 0, 0);
        ViewCellGrid.Children.Add(PLUNumber, 1, 0);
        ViewCellGrid.Children.Add(PLUDescription, 2, 0);
        ViewCellGrid.Children.Add(Price, 3, 0);
        ViewCellGrid.Children.Add(LastGrid, 4, 0);

        var nameLayout = new StackLayout()
        {
            HorizontalOptions = LayoutOptions.FillAndExpand,
            Orientation = StackOrientation.Horizontal,
            Children = { ViewCellGrid },
        };

        return nameLayout;
    }
}

I have an event which gets called view model is the page view model

void OnTapGestureRecognizerTapped(object sender, EventArgs e)
{
viewModel.PLUDetails.PLUDescription = "XYZ";
}

The view model is :

public class CalculatorViewModel:INotifyPropertyChanged
{
public SalesRegistrationViewModel SalesviewModel
{
get { return _salesviewModel; }
set
{
if (_salesviewModel != value)
{
_salesviewModel = value;

                if (PropertyChanged != null)
                {
                    PropertyChanged(this,
                        new PropertyChangedEventArgs("SalesviewModel"));
                }
            }
        }
    }

    public PLUDetails PLUDetails
    {
        get { return _pludetails; }
        set
        {
            if (_pludetails != value)
            {
                _pludetails = value;

                if (PropertyChanged != null)
                {
                    PropertyChanged(this,
                        new PropertyChangedEventArgs("PLUDetails"));
                }
            }
        }
    }

    private PLUDetails _pludetails;

    private SalesRegistrationViewModel _salesviewModel;

    public event PropertyChangedEventHandler PropertyChanged;
}

The PLUDetails class is:

public class PLUDetails:INotifyPropertyChanged
{

    public int SerialNo { get; set; }

    public string PLUNumber { get; set; }

    public string PLUDescription
    {
        get { return pludescription; }
        set
        {
            if (pludescription != value)
            {
                pludescription = value;

                if (PropertyChanged != null)
                {
                    PropertyChanged(this,
                        new PropertyChangedEventArgs("PLUDescription"));
                }
            }
        }
    }



    public double Price
    {
        get { return price; }
        set
        {
            if (price != value)
            {
                price = value;

                if (PropertyChanged != null)
                {
                    PropertyChanged(this,
                        new PropertyChangedEventArgs("Price"));
                }
            }
        }
    }



    private string pludescription;

    private double price;

    public event PropertyChangedEventHandler PropertyChanged;

    public string DiscountType { get; set; }

}

But my label is not getting updated. It is showing blank. Kindly help me in this. I am frustrated.