MBD PAYED UP LATER

hi I settled my Absa credit card that was handed over to MBD legal collection in December and I have been calling them for the paid up letter since December and to date I haven't received any letter and now every time I call thy tell me thers is an outstanding R13.08 sometimes its R18.00 sometimes is R15.00 and being told that thy requesting for my payed up later till date and can i have an email address where i can send prove of payment of this remaining balance thy keep telling me about.