Wrong billing by MTN

I had an MTN contract that was due to expire on the 27th of August this year, I called and cancelled it,later I saw a phone that I like and upgraded to the phone, I was informed I’d be paying 1499 a month for the contract and to my surprise they debited R29k and when I called them I’m being moved from one consultant to the next and nobody will tell me what is going on, the next thing they will black list me for their mistake, I’m still waiting till today to find out how much my monthly fee is to be, I’m angry and disappointed as this is the first time this is happening to me