Excel using cached data for linked cells

Excel appears to be using cached data in linked cells from a worksheet which no-longer exists, is there some way to stop this from happening?

='C:...[Nov.xlsx]Sheet1'!A1

No matter how many times I recalculate the spreadsheet this cell continues to display data from the now deleted `Nov.xlsx` workbook.

I have tried writing a VBA function to return the value of the linked cell but that appears to suffer from the same problem. This is called by:

=GetCell("'C:...[Nov.xlsx]Sheet1'!A1")

Private Function GetCell(ByVal sName As String) As String
    Dim FileFound As Boolean
    On Error Resume Next
    FileFound = (Len(Dir$(ParseCellReference(sName), vbNormal)) > 0)
    On Error GoTo 0
    FileFound = True
    If FileFound Then
        MsgBox ("sName1=" & sName)
        GetCell = Worksheet.Evaluate(sName)
        MsgBox GetCell
    Else
        GetCell = "n/a"
    End If
End Function