No explanation for data disappearance

I have had a bad experience with MTN a while back and had to pay a huge amount because they claimed I used the data, I think is was impossible for me to use so much data even if I was on the internet 24 hours per day, but I had to pay to get access to internet. Since then it has been going well but all of a sudden on the 6th and 7th of this month my data just totally went down a drain somewhere, I had to recharge 2 gig which also disappeared, and had to buy another 1 gig just to make it to the middle of the month when my data is replenished. I spoke to someone in the call center, she was very friendly and helpful but could not really give me an answer.<br> This makes me very unhappy because in the area where I live MTN signal is relatively stable, much better than the rest, which is why I have a data contract with MTN.<br> I want to know what I can do about this lost data, and this time around I want PROOF from MTN that I did use the data they claimed I had.<br> It use useless talking to their call center or accounts department, you just do not get logical responses from them.