Bad Service, cant explain why cancellation not processed

Absolutely no help from MTN and Mobile Plus. I returned their cellphone within 7 days as I no longer wanted the phone. I got debited for a cell phone I no longer have. I have been back and forth with MTN and Mobile Plus as to why the cancellation hasnt been resolved yet. I have provided them with the collection code on numerous occasions. now I am getting phone calls from a debt collector to say I owe them. Their call centre agents cant even explain their can cancellation process is so long. Its been 5 months now from the day I returned the cell phone but no assistance from both parties to do the cancellation. I have sent many emails and no help at all.