MTN *****ing my money!

I have been a client with MTN for 20 years and has the same number for 20 years. I upgraded my contract 2 months ago and since then the contract has been a mess! Mtn is *****ing my money!! On the 18/9/2019 I loaded airtime on my phone and had a total of 100 minutes, made a phone call of 7 minutes, and mtn took of 50 minutes! On the 19/9/2019 I made a call to the call center to report this( Ref ***) problem, and was told that they can see it is a problem on that line,and will investigate the problem. just after my call to MTN they took of 50 minutes again no calls were made. I then phone in again and was told that they still did not investigate the problem (ref ***) but will escalate it. for me that is unacceptable as now I don't want to load my account because they ***** my money! And in the meantime I can not make any calls because I have no minutes, what is the use of having a phone and contract. and there was a few time before this incident that I thought what happen to my minutes, but at that stage did not realize that mtn is depleting it as the like! BAD SERVICE MTN!