MTM don't take ***** seriously!!

I have been an MTN client for over 20 years. After experiencing no real problems over the years, this year it has gone horribly wrong! My monthly payment at the moment should be R297.00, but during for Jan, Feb, March 2021 it was R6 165.20, R6 740.44 and R5 940.45 respectively. The dramatic increase in my bill is due to the addition of a second cell number to my bill (078 number). This number was added without my knowledge and it isn't a number of mine or anyone I know. I reported this suspicious development to MTN and one of there "Service Champions" opened up a ***** case (ref: ***) on 12 March 2021. I have subsequently followed up and each time I'm told that the case is still open. After a month nothing has been done to resolve this problem and no reportback. MTM had no hesitation in billing me for the enormous amounts for January and February. Once I realised that nothing was being done to sort this out, I reversed my debit orders. Now obviously MTM want to disconnect me. This is shocking service!! Surely it doesn't take over a month to look into a ***** complaint and give some feedback to a client who has obviously been ****** by some *********. I want to close my MTM account as soon as possible!!