MTN is ripping me off

In 2015 i got a mobile wifi with MTN SA and in November 2017 i cancled that contract witch then was switched to pay as you go and i never used that number again. May 2019 that number was reactivated on my account "by the system" when a sim swop was done for another person. I have since been paying aditional costs on my MTN bill for something i dont have. This account im being billed for was opened in 1899 acording to their "system". I was told to get a affidavit from the police and send it to them........and still nothing has been done, i keep getting billed for it. I cant stop my debit order because then they cancel my phone and i end up getting bad credit on my name, but if they are billing you incorectly you have to jump through endless hoops to get your money back. MTN SA is ripping me off and there is nothing being done on their side. I have a assistand from my local MTN trying to help me but not even he can get someone from head office to sort it out, billing dep. seems like they dont want to help. I need help with this as this is *****ing with my budget