Cell c is robbing is dont buy data from them

Last night i checked my data remaining on my contract i have 16gigs of night data and 8,9 gigs on day data, then i checked my balance again at 8am it was 8,7, i just recieved a sms saying i have 1,8 gigs left.......cell c you robbing us how the hell can i use 7 gigs of data in a few hours, all i did was go on facebook and insta!!!!! When i called your pathetic call centre i was laughed at while i was on the phone with the agent my gigs were going down and i wasnt even using any apps!!!!!!how do i cancel this contract!!!! You are robbing me cell c!!! Time to change all 5 of my contract to a service provided that doesnt ROB me!!!