MTN - the company that *****s ordinary people

I cancelled a contract I took online with MTN , returning the phone (in original packaging) to the MTN store in Greenstone . I was assured the contract is cancelled. I started getting billed for the contract from Nov. I have tried to get MTN to rectify - but the billing carries on. I now have debt collectors phoning me and harassing me. All my phones on the contracts have been suspended due to this - totally unacceptable. MTN does not respond and when they do nothing happens. My credit history is now *****ed as well - and MTN DOES NOTHING .