MTN not canceling contracts and *********** clients

In Nov 2018 I signed a 24 month contract with MTN (a black Friday deal whereby I got the 50gb anytime with free 50gb night) at half price and with double the data. Basically I got 100gb anytime and 100gb night data for half the price of the 50gb package, R427.44 excl VAT a month. Fast forward to Oct 2020. I got calls from MTN advising me that my contract was up for renewal and each time I told the consultant who called me that I will not be upgrading and will be going prepaid when the contract ends. I then called the MTN call centre on 14th Oct as my contract end date was 22nd Nov (end of 24 months), just to make sure they knew that I was going prepaid and not renewing. I was told that I should call them on the 23rd Nov to cancel the contract as it ends on the 22nd Nov. However on the 11 Nov 2020 I receive my new bill from MTN and they have billed me R2905.15 excluding VAT. I called the call centre, and after holding for 30 minutes and then speaking to 3 different consultants was told that they cannot tell me why I'm being billed this exorbitant amount and that a bill query will need to be logged. Can this please be corrected as soon as possible as what you guys are doing are *******. I've had contracts with MTN for almost 20 years and I can safely say never again. When my other contract comes to an end I will not be upgrading it as well. You have lost yourself a loyal customer. The reference number for my latest call to your call centre is *** and I'm sure you should have a record of all the other times I called in advising that I want my contract terminated and to go prepaid at the end of the contract term.