It isn’t very clear what you are wanting, but I think this might point you in the right direction:
Sub foo()
Dim LastRow As Long
Dim LastCol As Long
LastCol = Worksheets("ComboBoxList").Cells(1, Worksheets("ComboBoxList").Columns.Count).End(xlToLeft).Column
'find the last column with data on row 1 (add 1 to this number to find the next empty column)
LastRow = Worksheets("ComboBoxList").Cells(Worksheets("ComboBoxList").Rows.Count, LastCol).End(xlUp).Row
'find the last row with data on the last column
Worksheets("ComboBoxList").Cells(LastRow + 1, LastCol).Value = Me.response.Value
'add the value of Response to the next empty row in the last column (empty row is lastrow with data +1)
End Sub