MTN refuses to switch expired contract to Prepaid

After my contract time elapsed with MTN, I have tried unsuccessfully to cancel my subscription with them for more than two months going now. Firtly I went to a store - which said they cannot process cancellation (or even assist in the process) I had to do it via their call centre. Every time I phoned in the tried to convince me to stay on as a subscriber - and not cancel / go on prepaid. They also insisted they cannot cancel my subscription because another department firstly had to cancel the dual sim I had linked. I spoke to this department (a couple of times) and every time they promised to cancel the dual sim. The call centre agents drops the call whenever you ask who you are speaking to. I am sure MTN is showing an increase in subscribers ONLY because they refuse to let anyone cancel their contracts when they run out. They probably incentivise their staff in such a way that they miss a huge opportunity if they cancel subscription of a single customer. If I knew they will take me hostage in this way I would NEVER have done business with MTN in the first place. Next call is to the ombud and then to SAPS to lay official complaints.