Struggle to cancel MTN contract

I had a MTN data contract. After 24 months, the contract is month to month. I tried to cancel this contract, but with no success. When I phone the 183 135 number, from my phone, which is another service provider, you do not get the option to speak to a consultant or to cancel a contract. If you go to a MTN store, they also tell you, phone 135, we do not cancel contracts. I phoned MTN in Mimosa, Bloemfontein, asking for assistance, and the lady who answered, told me it is not her problem. I sent emails to the retention department but still, no response. So, now I will have to stop it at the bank.