Interest charged on R 0 account balance

On the 10th of February I settled my credit card which had a balance of around R 7.8k. On the 22nd of February I received my statement and was a bit surprised that I was charged interest. As far as I'm aware an account that has been settled cannot generate interest. <br> <br> I called the call centre last week and spoke to a lady by the name Jabu (***) she told me that the interest was charged because I had made a cash withdrawal in January, when I corrected her that it was an online transfer made to my FNB account she indicated that Discovery views transfers as cash withdrawals. She later indicated that she would send me the breakdown of the interest charged. She could not indicate whether interest would still be charged in March if I again settled the account.<br> <br> After not getting any response as promised from Jabu I called the call centre again and spoke to a lady by the name Thuli (***) she too could not assist, after being on the line with her for 18mins she indicated that she would call me back as she was not sure why interest has been charged.<br> <br> All I need is to get clear and correct explanation as to why I am charged interest on a R 0 account balance