MTN charging past contract ending

My data contract ended about two months ago and before the new month started I said that I don't want to renew my contract. I was supposed to only be charged for my other contract. But somehow, even after a request was out it, I am still being charged for the contract that ended, only now, it's being done on a month to month basis, which obviously costs more money. I have been to the branch a few times, but still my account was credited with data etc this morning which means I will be charged again for the next month, which I did not give permission for. Previously I have not had problems with MTN. Since I moved to another town, this branch has been giving me problems. If it's not charging me for things I did not sign up for, it's continuously charging me for a contract that I ended. I don't recall signing a "till forever and forever" clause.