Terrible service

I Dudley Coetzee id ********** 091087 cell c number ********** 133 has got a Cell c Pinnacle unlimited account with Cell C whereby I get 10GB of Data unlimited calls and sms per month For the month of August My data got depleted and I cant explain how, but they said I went over with about 1,5 GB of data a month and Cell c want to bill me R1 384.00 for data for Saturday the 26th of August and I was told that there a a volantery limit set on my account that I didn't apply for. If my Data for the month is finish its finish but that amount is scary, and the fact that on the 26th they have charged me R930,70 at 4 minutes after minute for for 1GB of data what day lite *******.How can they just right up services with you without explaining anything with you.