Mtn bad service

Unhappy with contract cancellation process, went to menlyn mtn branch to cancel contract and was told to cancel over the phone . 2 days before month end I called in and was told that I need to go back to the branch with their FU devise to cancel. when went to the branch on the 3rd which was a Monday and they cancelled the contract now im getting messages to say they going to deduct R500 and something. When I bought the device they took pro raya. Now I need to pay full amount without using the data. Why was I delayed on purpose. I was given wrong information from the start. I can’t pay for data I didn’t use