Overcharge for Data

MTN has charged me more than R3000 extra for data. My 1st realisation that there was a problem came when I received a message on my phone to indicate I had used 90% of my credit balance. This came through while my computer wasn't even on (and hadn't been for a while). The next message I received was that my devices had been blocked due to my full credit limit being used (almost an hour later while my computer was still shut down). I don't see how it was possible I was using all this data when my device was not even on. Also, the last screen on my MTN online app said I had 2.7 gigs still available. Attempts to complain by phone have got me nowhere and email complaints go unanswered. Noting all the consumer complaints related to data of late, it seems to me that MTN is blatantly ripping customers off with no end in sight.