Incompetency in trying to close account

I've been trying in vain to get my credit card closed after settlement. I've have spoken to Natasha from credit card division but she lacks basic logical understanding and is absolutely horrible to deal with. She doesn't even give a customer a chance to speak. I paid an amount of R12000 into my credit card on 23/10. On 24/10, i did a payment of R10575. On 31/10, I requested for a settlement letter which was given and valid until 06/11. The settlement of R97470 including interest was done on 05/11 and cleared on 08/11. On 09/11, i logged onto internet banking and saw that i had R1100 available in credit based on the R12000 payment done. I transferred this out. What i do not understand is why interest was capitalised on my statement on 13/11 for R1224 after my account was settled in full on 05/11 which included interest. I've been trying to explain this to Natasha who just does not understand. The charges on 13/11 needs to be reversed and the account/ card closed urgently.