TOP UP DATA of R399/m ends up to be R5500!!!!!

Ive taken out a data contract of 5G per month for R399 (including a router), my account was significant higher each month and I had phoned several times to make sure that they have transferred the account to a top up contract. They did inform me that the data might run over if for example I download a movie, it will complete download before it will indicate that the data was depleted, but seriously R5500????? I phone customer care and they sent a request for audit, but this will taker 14 days? I still have device and need it for work not knowing what my next bill will be. They also just deduct the money and I still don't receive my billing via email as requested more than 10 times already. (I receive via MMS). I asked for a cancelation of the all my contracts...