Case Statement and Dates

I have some VBA code that goes sort of like this (Excel 2016)

Dim ccase as string

ccase = me.cboCagatory
Case Select
Case cccase = One
Me.txtDueDate = me.txtStartdate + 56
Case ccase = two
Me.txtDueDate = me.txtStartdate +14
Case ccase = three
Me.txtDueDate = me.txtStartdate +7

etc#


it si not exactly like this as I dont have the file on me but it appears the txtDueDate keeps coming out mm/dd/yyyy i have tried the format(me.txtDueDate, "dd/mm/yyyy" but it still dont work
I would be most grateful for any advise as Dates appear to be a problem with Textboxes. I started with 30/12/2017 and with ccase one 56 is ok comes out 25/01/18 with ccase two comes out 14/01/2018 but with 7 it comes out 01/07/2018 not 07/01/2018 why?

Many Many thanks

Thanks for your suggestions guys. I wish MS could put a date box feature instead of a text box.