Hotel California- you cannot check out of a MTN contract- even after expiry

It seems like MTN purposefully try and make it near impossible to terminate your expired contract. I got sms's etc to confirm my contract expiry and that I would in future pay more. I want to change to prepaid. I went into the MTN branch in Cape Road Qheberha. They could not terminate the contract, it was too old. I had to call 083 135. I have called that no so many times, it cuts you off after 5 minutes. Shocking service MTN. Please cancel my contract.