Settlement letter and paid up letter

I have requested settlement amount with FNB and I had settled the amount stated on the letter but I receive calls from their agents stating I owe the balance of R700 where as I paid the full settlement amount that was stated on their letter.

I requested paidup letter I haven't received it till to date . The matter was escalated to Legal dept and their Legal dept escalated it to collection dept but not a single response from them nor the paid up letter received. I want FNB to send me the paid up letter and sort out my credit status .