Nedbank Bad Internal control

I have never been so irritated ???? by Nedbank Credit Cards Division- in January 2019 the 7th i requested a settlement amount to close off the credit card, they then give me the amount outstanding and I paid this amount immediately. And the following day I called again to close the account because I could see on my bank app the amount was till reflecting- they then close it off and the amount was zero- six month later I get a call that I owe 1200 of interest and they now taking this to legal- What the hell is wrong with this Bank.