Data keeps dissaparing

So about a month ago I had my data and airtime depleted in the middle of the night while my data and applications were off. I called MTN to rectify this and get reimbursed, I was given an excuse o background applications and all that jazz. I have subsequently switched all applications and not even using my data, 3g and cellular data is OFF, (using work wifi at the moment.). I then make a phone call and after that I checked my airtime, at which point it was sitting on R147. 2 hours later (again my data is still off using work wifi), I get a msg telling me my data is depleted. I check my airtime only to realise my R147 is gone and the 500mb I had is also gone. MTN needs to reimburse me this time as they cant use an excuse of my applications. My phone is sitting with 3g off and I have not made a call. I need my money back NOW because I cant keep being *****ed like this without a reason. Customer service says there is no movement in my account which means nothing happened. I WANT MY MONEY and DATA Back this time, I am not letting this one go like the first time one month ago!!!!