Impossible to cancel unused contract

I have been billed for two discontinued month by month contracts which I want to cancel. I have been to an MTN in Howard Centre Pinelands and they were unable to assist me. I had to then phone MTN and have made five attempts so far. After receiving asssitance I was then transferred to the cancellation department and in all five attempts my call was dropped after about 12 minutes of waiting on-line. This is appalling service and I am very anxious to cancel these contracts as soon as possible. I will never use MTN again.