PAID UP LETTER!! ****

SSDA is a ****, I was handed over by Cell C and I made monthly arrangements to pay. In December I asked for a settlement letter and I settled the account on the 15th. I have been calling and asking for my paid up letter for 3 months now. When I call Cell C I was told that my account still shows in areas and It is not settled. Where did the money I paid go to? if Cell C has not received it in 3 Months????