high billing on data

On several occasions i have queried with your call centre on the high data usage on my data bundles. Upon browsing ive calculated that m cjarges 2mb per minute approximately. I only use the internet application and log onto face book but for a minimal timeframe. I dont post or view or downlaod anything. If i use google its only to search. Today ive used the internet application for 5 mins and approx 50mb was used. This is ridiculous. Yourccall centre cant assist in deducing why the data bundle gets delepleted so quickly. I only use data over the evenings as i use wifi during the day all day. Can someone please help as prior to this i was on the mtn network and never had a data issue. I migrated ft o vodacom thinking the network and service is better but clearly not.