MTN airtime continuous theft

I am a prepaid customer. I have been with MTN for more than 10 years. I have experienced in the last 2 months at least 4 occurances of my airtime mysteriously disappearing with the standard response of 'internet sessions' being the reason for the airtime disappearance. 2 -3 weeks ago I loaded airtime and it once again mysteriously disappeared and when I called the help desk I was told to switch my phone off and that they would reset it on their end as they had been experiencing technical problems. Once again on the 23rd of August 2015 I loaded airtime and it mysteriously dissapeared and the excuse was once again 'internet sessions' and 'auto updates' being sighted as the excuse for the disappearance. The next day 24 August 2015 I purchased an additional 60 rands airtime which I did not receive the full value of the 60 rands worth which I was also told included the additional 'free 60 mtn to mtn bonus airtime' that also was used up in less than a 24 hour period. I spoke to 3 different agents who told me three different internal processes that did not correlate. From a customer's perspective MTN has not met their service obligations and I am a VERY unhappy customer!