MTN - CANCELLATION: WAITING FOR 7MONTHS

I took a phone on contact out in September for an iPhone 13 Pro. It arrived on October 8th. I realized I didn't want it anymore. I returned it to the nearest MTN store on October 9th. I called the contracting company to let them know I returned the phone. I even received an IRMS number 585 914, which confirms the phone is has been returned. I have since been billed for this contract that I don't have. MTN has indicated that I own them R6600 for a phone I don't have nor have ever used it. I have been calling and being given the run around since October 2021. They are threatening to cancel my existing number even if the fault is on their end. The lastest ref# from MTN 1- ***0. Ref number for the rewards company Reference : [#***]. They have been saying that they are getting this canceled for the past few months and nothing is happening.