Remove excel validation list vb.net

Private Sub DeleteDropDownList()
        Try
            Dim xlApp As New Excel.Application
            xlApp.Visible = False
            xlApp.ScreenUpdating = False
            xlApp.DisplayAlerts = False
 
            'Open book here
            Dim xlBook As Excel.Workbook = xlApp.Workbooks.Open("FullPath")
 
            'Get sheet here
            Dim xlSheet As Excel.Worksheet = xlBook.Worksheets("Sheet1")
 
            'Get data used last row
            Dim lastRow As Integer = xlSheet.Cells.Find("*", SearchOrder:=1, SearchDirection:=2).Row()
 
            'Select the delete data range
            Dim cellRange As String = String.Format("AC{0}:AC{1}", 1, lastRow)
 
            With xlSheet.Range(cellRange).Validation
                .Delete()
                'xlValidateInputOnly=0  xlValidAlertStop = 1 xlBetween = 1
                .Add(Type:=0, AlertStyle:=1, Operator:=1)
                .IgnoreBlank = True
                .InCellDropdown = True
                .InputTitle = ""
                .ErrorTitle = ""
                .InputMessage = ""
                .ErrorMessage = ""
                .ShowInput = True
                .ShowError = True
            End With
 
            xlBook.Save()
            xlSheet = Nothing
            xlBook.Close()
            xlBook = Nothing
 
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Sub