Extra charges after I paid in full and requested closure of account

I have phoned on the 27th of June to get my settlement amount. It was given to me and I have also asked that an settlement letter must be emailed to me (only received it on the 16th of July). After I've received the amount, I paid my RCS account in full also on the 27th of June as the settlement is valid for 5 days. The lady also told me to phone back after a few days for the payment to reflect and then they can close the account. I phoned back on the 4th of July to close the account and the lady said she had sent through a request to close the account for me, only to receive an settlement letter on the 16th of July, 19days later and a statement with extra charges on, after I have paid in full and requested to close the account. I tried to phone but no answer both times i called holding on for 10minutes. I will not be paying the extra charges cause i have paid in full and requested that it must be closed. Someone didn't do their work properly like usual! I will be taking this matter further if the account is not closed and the extra charges removed ASAP. Also I would like a letter stating the account is closed and R0 is owed