MTN Ridiculous service

My mtn contract ended on 24 December, i received an sms stating that it will now be month to month. I tried calling mtn and with no luck kept holding on. I then sent an email on the 24th December confirming that mtn should cancel said contract as I do not require the month to month contract. I received an email on the 26th December confirming that the case is with retention as well as an sms confirming that the query has been closed. This contract was taken out for my mother so I have no access to the phone or anything that happens on it. I happened to check my mtn app just to see that they are charging me R198 (R89 is for my data bundle), I asked my mother if she got the data bundle and she said yes (she didn't know she wasn't supposed to get it) The case was with retentions on the 26th December yet by the 15th of January the contract was credited with the bundle? I tried calling mtn again only to be told that I need to pay for what had been credited and they will put me through to retentions... its been 3 weeks since I've been trying to get hold of retentions, an email was also sent not long ago and still not response. Please can you give me a call back because this service is unacceptable. My debit goes off on the 15th and I am only paying for my R89 bundle... mtn will be liable for any further bank charges should a higher amount be debited from my account as this is a query from 24 DECEMBER 2020!!!