NOT FRIENDLY AND NOT HELPFUL - TAKE OWN SWEET TIME

I had a TFG account with a balance of R435.90 03 Nov 2020 i paid the payment of the full amount on 19.12.2020. Contacted TFG to confirm if they received my payment they inform me that they did and that my account balance is now 0.00 i requested a paid up letter they then told me my account was sold to DMC on 16 Nov 2020 and i should contact them for the paid u letter. I contacted them regarding my account and the letter they informed me that i have a outstanding balance of R4103 on the account and that i am not paid up... How the hell can that be... I told them i paid the amount owing to TFG they insist that TFG must provide the Paid up letter. I raised a dispute as they still say i owe money ive been waiting for weeks for a reply ... as to why the amount is so high by them when ive already paid it and to when i will get a paid up letter.....