Paid up letter

The service is bull ****, I'm tired and annoyed.I had an account with Mr price and they are collecting for them,everytime I pay via eft payment they say they can't find my payment,I need to send proof while they are adding more interest as if I didn't pay.Last month again was called by an agent calls are being recorded go listen to the call as agent advised R 1503.00 will be debited on the 30th ,I gave her my account details and no debit order weren't through .I then decided to pay via EFT and they called yesterday stating I didn't pay I sent proof of payment .I haven't received my paid up letter at per promised instead interest is added and I have paid and sent proof . I'm tired please rectify and send paid up letter.