cell data packages up to Sh....

Got a new wifi router with 20 gig data day and 20 gig data nigh***** the fifft of August 2018 and 20 gig gone.Only my daughter used the router.She is 16 and normally uses about 4 gig data a month.Me also. I loaded R299 worth of data on the fnb app to my contract at cell c just find out I canmot do this on this contract.They did not tel me this.R299 gone.I phoned them.about 5 or 6 times to find out what is going on becuase 20 gig in 5 days is impossible.Cell C cannot answer me.I want to cancel this contract emediately I only got the contract 2 weeks ago.I need an explanation from them.They have so many excuses .I need answers from them why they hide things from the clients.