Cancelled contract in time - still receiving bills (and now attorneys)

My 2 year contract expired in April 2017. May I add that this account was never in arrears. I mailed my cancellation to MTN in March after THEY phoned me to enquire if I wanted something else seeing that my contract was going to end. I very clearly told them that I am cancelling the contract. I also send 3 mails after that to MTN Customer Service informing them that the contract must be cancelled. I also put a stop order in at my bank knowing that these service providers simply continue to deduct from your bank account. I would say approximately more than a month ago the calls from Norton attorneys started. I contacted MTN AGAIN and send all the proof that I cancelled the contract in time. I send this to the attorneys as well. I continued to receive phone calls from the attorneys as if they never received my proof of cancellation and merely responded that they can only go on the clients instruction. I at this time was insensed. I posted on FB messages to MTN, I tried calling the legal department to which I was told that I can merely give them my phone number and the legal department will contact ME. Needless to say - no phone call. I received another bill today from MTN merrily continuing to bill me. It is 7 months later...how on earth do I stop this?!?!? I am at my wits end. This contract was an Autopage that was taken over by them. Lesson learned...stay away from MTN...it is impossible to get hold of them via their support line as well and on their e mail there is no response whatsoever. So, I guess we will have to go to court or something because this nightmare is not ending!