MTN Online de3biting for cancelled contract

I purchased a black friday sale through MTN online. The device that was sent to me was not working and I decided to rather cancel the contract within the 7 day grace period as stipulated by the consumers act- well within my right! I went to MTN El Ridge centre where the staff very kindly assisted me in returning the device and sim card by completing a returns form to cancel the contract and sending the device back. It is now February and I am still receiving debit orders and legal threats from MTN. I have tried MULTIPLE times to contact MTN online to resolve this matter but constantly get hung up on the minute the words "Contract cancellation" are heard. I have all reference numbers from emails, phone calls and paperwork from the cancellation. This is clearly a very common issue as every time I am in the store to try and resolve this there is atleast another person with the same issue. I do not have the device or Sim Card- Stop debiting my account