Bad customer service

Since my son's cellphone contract that was on my name ended, I've been trying to end the contract for the data that my son received every month. I've been phoning and phoning, they put you through to cancelation department but when the phone gets picked up nobody is talking, you only hear voices in the back ground. Then eventually I hang up cause nobody is talking. MTN has very bad customer service, where they don't even allow you to cancel a contract. I NEED TO CANCEL THIS CONTRACT. MTN has almost never have signal in the area we are staying. My son is expecting very important phone calls for job interviews. I need to port my son to a new network, where he is able to receive phone calls.