Unable to explain high data charges

My contract was due for an upgrade on the 17/5/2015 I went to Clearwater mall Vodacom shop I upgraded to a Samsung tablet 2G data for R299 a month. My account was debited for R1737.18 on the 22/5 I locked a query with customer care the consultant Thabo phoned me back and said Vodacom will not be able to explain the high data usages on the 17/05 on one day I used R728.78 data I need someone to explain what was downloaded on that day. There is also a laptop 3G instalment for R166.67 I DONT HAVE a laptop no one can explain this charge to me. I'm not unwilling to pay but surely Vodacom needs to explain the high bill and data usages to me. This month I downloaded and used my tablet 500 times more and still have 868MB left how is this possible. I requested the team leader to phone me back I was promised Marlon or Sasha-Lee will phone until now no call has been received. VERY VERY disappointed with Vodacom and the service I received.