MTN ****ming me

MTN just converted my contract to prepaid few months before it should have ended. When I call I am moved from one department to another and no one can explain. I am still paying for the contract but am on prepaid and no one can reverse it. It’s been almost 2 weeks of calling them and no one helps. One promised to call back but never did. Some tell me they don’t understand what happened. No one is willing to assist me