Mtn *****ing money

On 1November 2015 I cancelled my Mtn uncapped data contract and requested to cjange to pre-paid.As expected the service was cut a couple of days after that but not switched to pre-paid.just no internet access.After that Mtn still deducted R314 for 3 months.Afyer I complained and asked for a refund,the saleaman told me they said I had used the internet and they will not refund me.He also said that this is a general problem and I would probably only get joy by going to the ombutsman.I asked for itemised billing on this account but so far no reply and no answers.think this is ******** and I find it very frustrating when they just deduct money for no service.You might as well come into my house and ***** R314 out my wallet.What is the difference????