Delay/Refusal to cancel already expired contracts

We took out 3 cell phone contracts with MTN in April of 2013 which expired at the end of May 2015. We were advised to send an email to [Email Removed] 30 days before expiration to inform MTN of our intentions not to upgrade or renew. On April 15, 2015 and again on May 1, 2015 we did so. On both emails we received a delivery and read report. After numerous failed attempts to contact the customer care line to follow up on the matter we finally received an email reply on June 15, 2015, during which I was asked to complete a cancellation form and send it back along with a copy of my ID which I did on June 16, 2015. I once again received a delivery and read report. Despite many efforts to contact MTN via the customer care line, email, personal visits to our local branch (Lydenburg, Mpumalanga) and FB these contracts have still not been cancelled. The customer care line doesn't answer the phone, nobody replies to the emails and the MTN branch informed us that they are unable to cancel contracts. Reference no given: *** (June 6, 2015). Ref no given: *** (June 10, 2015). It is now June 22, 2015 and I have still not heard anything from them.