Overcharging data consumption

Am ****ed - last night I turned my data on for whatsapp and just went on Facebook and Instagram for about two minutes and I checked my balance this morning and I see I used about 400MB in one night?? And I turned my background apps off and they were closed. It's costing a fortune having to keep recharging my account and stuff - not the first time my data is going extremely fast. Vodacom what the **** is going on with you??? I am a student and can't afford this!!