Bad Service from MTN

I have a cellphone contract with MTN which I missed payments and was handed over to their MBD INC attorneys last year Decemeber 2019 .I then made arrangements with the attorneys and have succesfully completed the payment and even received the paid up letter.I then sent the paid up letter to *** now my problem is MTN is now telling me **** that they havent received any money from MBD INC attorneys and wont clear my name.This utter nonsense I want that R1750.00 to stop appearring on my credit bureau profile.MTN needs to sort out this mess