Depletion of data with no reason

I had my data depleted on Tuesday 07 September 2015.<br> within the next 24 hour I loaded 300MB data that has been depleted by MTN. I called in 3 times and all they can tell me is that I have not used that data and they will investigate and I must call back in 3 days.<br> I am left without data and cannot load data and MTN cannot help. I am utterly disappointed at the service.