Cancellation of MTN contract nightmare

I got a cellphone contract belonging to my late wife that needs to be stopped and convert to prepaid as the term expired. It is easy to take out contract but just try to cancel it. So lets try it this way as I phoned 135 and spoke to retention department but call was dropped and not sure it was done as he only tried to convince me to upgrade a contract I do not need. Tried to phone again but after almost an hour I gave up. Send them an email but MTN does not even bother to answer. The branch also tried to phone 135 and gave up. Is there anyone at MTN that does want to work and help me to cancel the contract and make it prepaid and may let me know how long does it take.