bank account debit

I had a contract with mtn which expired in Sept this year. I have called them countless times to cancel contract however they we still debiting my account while I made the cancelation. The next thing I call in this morning at around 6:00 and got through to a lady who was so not helpful I asked her to assist with the matter she told me I need to call 808 but since my number was changed to pre paid I couldn't get through I told her to get me a supervisor as they might have helped she told me there was no supervisor on the floor and instead of giving me an alternative she hung up in my ear. I need to be contacted tearing the matter because I am not happy about the service I'm getting. I'm at the point where I even gel like going to a competitor because of this terrible service I have recently from them.