Paid up my account but told to pay more

I have been paying my FNB loan through Debt-In, which i owed around R2800 and i was told that in order to settle my account i have to pay R835 for Three months , they started debiting R500 in March then R835 from April to June 2020. I called them for my paid-up letter after the June debit order and i was given a run around, next thing they called me to remind me of another debit order when i told them i was done paying and waiting for my paid-up letter , i was told that Arishna will call me because she is the one that was handling my account. 4 days later and I still have not received any call from anyone. now they send me a reminder message for another debit order. this is not fair I want my paid-up letter before close of business today.