Contract Cancelation Issues

I've tried unsuccessfully to cancel my MTN contract. I have received a reference number RCO136005, indicating that they have canceled it, but the bill keeps coming off my account and I cannot get through to Retentions Dept to see why. The contract was a sim only deal, which I was told was month to month and could be canceled at any time. I think MTN is definitely very poor on customer service. They don't want to allow people to leave, instead they want to frustrate the customer, so that they won't think of coming back.