MTN account ****med (***** on MTN cellphone contract)

I am so disgusted with the service from MTN. My Mother was ****med R14k on her cellphone contract when she was called by a man claiming to be from the MTN ***** department and saying that someone is trying to do a sim swap. Unfortunately the man was given the OTP (I realise now this should NEVER be shared). The issues I have with MTN are: HOW does my Mother; who is a pensioner; qualify for a credit limit o R14k (which was capped at R2k - the ******* (from ONE OTP) was able to raise the credit limit to R14k and spend it within 2 mins on data and various other purchases. We were at MTN Centurion branch and blocked the number and here is where I have my 2nd issue: MTN assured me that the ******* could do no further damage and they unblocked my Mother's number. Later that day about 20 vouchers (apparently purchased via the MTN app) came through on my Mother's phone. So go back to MTN (Mall@Redds branch as the branch in Centurion where we went told us they had no internet and could not help us). At the branch in Mall@Redds I insisted they change her number. Initially the MTN lady who assisted us did not want to change her number and they told me it would cost R250 to change her number; which they subsequently did - note that the number only was supposedly changed; not the simcard. On Tuesday (this is now the 3rd day in a row) back to MTN. It seems my Mother's old number is still active (she is still getting messages) and it now seems as though her sim card has been cloned as she got a sms stating her handset had been configured. So we will be going back to MTN for the 4th day in row today.' All of this happened after sharing ONE OTP! There really seems to be no cares given or any real attempt to help. The response from MTN (both Centurion and Mall@Redds branches) is that "you shared the OTP" so basically this is all on you. I am convinced the ******* is an employee of MTN as how on earth did he know what my Mother's credit limit was that she qualified for - that she had capped at R2k so he knew how much he could raise her limit to - and how was he able to perform multiple transactions and purchases from ONE OTP that was shared?!!! How on earth can you as the CUSTOMER not determine what your credit cap is - their response to my question on how on earth did a PENSIONER qualify for a R14k credit limit - MTN"s response: she has a good credit rating! Why was a simswap not done immediately by MTN staff? Why are you charging R250 for a number change when the sim card wasn't replaced? Why do I keep getting assurances that the ******* cant do any more damage as he only had the one OTP yet 3 days later my Mother is STILL getting messages of activity on her account that she has not done. I am so shocked and disgusted by the service from MTN and rest assured my Mother will be moving her account as soon as it expires!!!