macro won't auto trigger on cell change

Afternoon,
I have a spreadsheet with rows 20 - 34 having two merged columns B-E and F-J (I know nobody likes merged cells, but i need it to be this way as the people who are using the spreadsheets are proper novices and therefore rubbish at entering information correctly.)
I have managed to cobble together a macro that auto adjusts the height of the columns to auto fit the text.
This works by comparing the merged active cell text length LEN with the other in the same row and if it has more text then adjusts the height to fit. See the code that compares and trigger the actual resizing code below:

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Const WS_RANGE As String = "B20:F34" '<<<< change to suit

On Error GoTo ws_exit

Application.EnableEvents = False

If Not Intersect(Target, Me.Range(WS_RANGE)) Is Nothing Then
Dim LenValue As Integer
Dim LenValuenext As Integer

With Target
'rhods bit
LenValue = Len(ActiveCell)
LenValuenext = Len(ActiveCell.Offset(0, 1))
If LenValue > LenValuenext Then
Call height
Else: GoTo deadwood
deadwood:
End If

'end of rhod's bit

End With


ws_exit:
End If
Application.EnableEvents = True
End Sub

and that triggers the code to actually do it.

Sub height()
    Dim CurrentRowHeight As Single, MergedCellRgWidth As Single
    Dim CurrCell As Range
    Dim ActiveCellWidth As Single, PossNewRowHeight As Single
    If ActiveCell.MergeCells Then
        With ActiveCell.MergeArea
            If .Rows.Count = 1 And .WrapText = True Then
                Application.ScreenUpdating = False
                CurrentRowHeight = .RowHeight
                ActiveCellWidth = ActiveCell.ColumnWidth
                For Each CurrCell In Selection
                    MergedCellRgWidth = CurrCell.ColumnWidth + MergedCellRgWidth
                Next
            .MergeCells = False
                .Cells(1).ColumnWidth = MergedCellRgWidth
                .EntireRow.AutoFit
                PossNewRowHeight = .RowHeight
                .Cells(1).ColumnWidth = ActiveCellWidth
                .MergeCells = True
                '.RowHeight = IIf(CurrentRowHeight > PossNewRowHeight, _
                CurrentRowHeight, PossNewRowHeight)
                .RowHeight = PossNewRowHeight + 3
            End If
        End With
    End If
End Sub

to get it to work I am having to trigger it from the worksheet_selectionchange. This only works when you click on the cell and not when you add/remove text.
I have tried triggering from worksheet_change, but absolutly nothing happens (not when you type, not when you click.)

does anyone know why and how to fix it? This is sending me absolutly mental.

Thanks in advance.