Settlement Complaint

I called Nedbank and requested a settlement letter for my Credit Card. I received the settlement letter and immediately settled the account. After settling the account I called Nedbank to confirm where I can send the proof to that I destroyed the cards. Nedbank then contacted me back saying that the settlement amount provided was incorrect. The manager that contacted me asked me how could I think that the amount was correct. As a customer they cannot expect me to assume a settlement amount is incorrect after requesting written confirmation. I then sent an email to the complaints department for assistance in sorting the matter out and getting the account closed. The complaints department was useless and is refusing to assist me any further. I even asked for a generalor operational managers contact details and the agent from the complaints department refused to further assist me. I cannot be held liable for a mistake made by Nedbank.