Impossible Contract cancellation

I had a contract with mtn, it is data only and costed about R700 per month. This contract ended in november and i have been trying to cancel it. I even tried to cancel before but there was a high cancellation fee. Since last month i have been calling their cancellations department with no joy, they keep calling for upgrades but nobody to help me cancel. Now i have gotten a statement for December saying i must pay R3000, for this contract that i have been trying to cancel and data that i dont even use. Horrible service which is why i am cancelling and taking a new contract somewhere else. I refuse to pay the R3000 for a contract that was completed and now sky rocketed. I refuse to spend another hour on hold trying to cancel this contract. This people will rob you of your hard earned time and money. If i have to walk into a branch and make a massive scene then that is what i will do. Horrible service.