Not allowed to ever cancel a contract

I want to cancel one of my 3 mtn contracts. The contract has expired and is for LTE. But I now have fiber at home. However, MTN makes it impossible to cancel anything. Their call centers or emails do not reply, they give no contact number and the shops are not allowed to process cancellations. I have been a loyal customer for more than 3 years with a bill greater than R 1000 per month. Yet they do not want to help at all. It must be ******* to not allow a contact to be cancelled. In the time of corona they must support paying customers better, to help them manage their cashflow with unnecessary contracts