Sim swap

I can not begin to express how frustrated i am with Mtn in January this year after my contract ended and was due for an upgraded they decided to give someone a contract phone under my name fine that was sorted May 4th a sim swap was done on my number called in and reversed it and added my number on their watch list but they still allowed another simswap to be done on the same number on the 18th of May still did the same process of simswap reversals and even changed the sim card but that didn’t stop mtn to allow a simswap to be done on the 24th of May which gave the ****mers access to my bank now i need a clearance letter to state that a simswap was done so the bank can investigate Mtn can not give me the letter from the 28th of May till today i dont have the letter while the inconvinience was on them to begin with how was a sim swap allowed 3 times even when the simcard number was added on the watch list