R19000.00 account

we have a vodacom red account a talk 500 and 3 top up account for my kids, this month the top up account got billed R13000 on data alone. it is supposed to be limited to 2 GB per month. you can not win with these types of service providers, do we sue vodacom and where do i start? for the past 3 years my average monthly account was 4500 to 6500 every month. do i have to change to cell c and hope for a better honest accounting system ?