MTN Contract cancellations a Big Mess

I had an data contract with MTN for 2 years. So when we reached the end of the contract we called the call centre to cancel the contract in Jan 2021 but now we have a bill of almost R20000 and they just keep on saying that we have to pay it in full before they can cancel the contract, but in the meanwhile they keep on adding to the bill, but we dont even have the simcard or the device any more, because we thought it was cancelled.