Changed your function to this.
Function FindLastDateCell() As String

Dim c As Integer, lttr As String

Range("B2").Select

    Do Until IsDate(ActiveCell) = False
        ActiveCell.Offset(0, 1).Select
        c = c + 1
    Loop
    c = c + 1
    lttr = Split(Columns(c).Address(1, 0), ":", -1, 1)(0)
    If c > 10 Then
        firstcol = Split(Columns(c - 10).Address(1, 0), ":", -1, 1)(0)
    Else
        fisrtcol = "B"
    End If
    FindLastDateCell = firstcol & ";" & lttr
End Function
In case lastcolumis AD it gives you 
FindLastDateCell = "T;AD"
In your Port code I changed

lttr = FindLastDateCell
to this

    firstlttr = Split(FindLastDateCell, ";")(0)
    lttr = Split(FindLastDateCell, ";")(1)
Which gives you firstlttr = "T" and lttr = "AD"
Now you can play around with both variables to suit your need.