Troubles with cancelling my contract and MTN disabling my SIM card before the expiry of the contract

I have been trying to cancel my cellphone contract for the last two months now, requesting cancellation quotes from MTN to see how much it would cost to buy out my contract. I was sent from person to person and nobody was able to assist. Eventually after dealing with numerous people I received the quote to cancel the contract before its expiry and it was significantly more expensive to pay to cancel the contract compared to keeping the contract for the remaining months and continuing to pay the monthly fee (which makes no sense since if I pay them up-front for the rest of my monthly fees they can earn interest on this lump sum, which should make the buy-out cheaper). I decided to rather keep the contract until its expiry at the end of May. They have now cut off my service, disallowing me from making calls or using the data that I continue to pay for. I have had an on-going contract with MTN for over 10 years now and this is the response when I try to move to a different provider to cut costs; it is absolutely pathetic. There needs to be better regulation over telecommunications providers as they do not care about treating their customers fairly.