I was DE*****ED under MTN's watch

I have been an MTN customer for over 20 years and have 3 active contracts with MTN. On the 6th of April 2021 one of my data express contracts (the 4th contract) expired and I called MTN Call centre to cancel that particular contract and that was successfully done. The consultant confirmed that my monthly tariff will now be reduced to approximately R622. I became very concerned when only 2 days after cancelling my line I received a strange SMS stating that a credit limit has been set to approximately R19 370. This was very unusual as I never knew that there is a credit limit and I became very concerned about what seemed to be ******* transactions which was clearly being conducted without my consent. On the same day, I rushed to MTN Cornubia Branch and reported all these strange incidents, a consultant checked and advised that I go to MTN Coastlands Branch. At about 14h30, I went to MTN Coastlands and again I expressed my concern over the strange and malicious sms's that I received. The consultant investigated the numbers on my sms's and tried to possibly trace the sources and I was then advised to do an affidavit explaining the above and give to the consultants at Coastlands for further investigation. The consultants also zero'd my credit balance (Which I never knew existed) and also confirmed that I have indeed cancelled 1 contract on 6 April 2021. To further acquire peace of mind after this, I called the call centre (Reference ***) and spoke to Mr Seasor Dawning about the encounter and proceeded to check and assure me that there is no malicious activity that was recorded on my account despite me verbally explaining the examples of the the strange sms's, and Mr Seasor assured me that he has zero's my limit balances and that all is safe on my account and I need not worry. My estimated monthly tariffs through debit order is about R620-R720 p.m and I still do not understand until this day why then my account reflects that I am owing money to MTN as according to my knowledge I have never made a request to increase any "credit limit" and therefore request for MTN to explain and investigate how that happened without my consent. I demand answers from MTN in this regard. I feel that MTN is being unfair to me by expecting me to pay an amount of money that I have no knowledge of!