FNB Credit card

I am struggling to close my FNB credit card. I settled the balance and sent them email to close my account on the 3rd December 2018 . They rep**** that I have to pay a certain amount as it has a debit balance. I transfered the amount and send them email on the 5th to close the credit card. They didn't reply . On the 11th I recieved a statement , they charged me a monthly fee and interest . I am now owing them . I don't understand why they don't close my account. I called them since last week but still there is no change.