Cancelling a contract

2 contracts cancelled last year and MTN are still billing me every month. Rivonia office can't help as they only deal with new contracts ( been there 2 times), the customer care is not responding to my emails with the correct information ( so many emails), customer complaints do not respond apart from an automated message which assures me that they will respond within 48 hours ( I've given up on them).I have tried on several occasions to call their cancellations dept and they either don't answer or I have waited 35/25/40 minutes for them to answer. I recon I've been a customer of MTN for over 20 years and they treat me like this. They are not even interested to know why I am cancelling contracts as I would willingly give them feedback to improve their business. So the last thing customer care told me yesterday telephonically was that I will be called back within 2 hours. I'm still waiting but didn't honestly believe they would. It's not a huge amount of money they owe me but it's the principal - they were happy to take my money all these years and now they don't want to give me back what they owe. I have 2 other phones with them that I am cancelling as soon as the contract expires. They must be the worst 'service' provider in SA