Internet data suddenly used up very rapidly.

We have had a wireless telkom phone for about 2,5years, with 10GB data a month. We noticed on about thge 12th May our data was used up, thats 10GB in 12 days. We only do internet browsing, no downloading of movies, music etc. We thereafter purchased a once off 3GB, which was used within a day with us hardly even using the internet. Then on Sat 23 May we purchased a 3GB again at 7am, we used it at 7pm, at 7:30pm it was used up. This is the first time in our 2,5 years that this has happened. All devices auto updates are switched off, its just 2 of us at home, with 1 tablet, 1 netbook, and occasionally 1 smartphone uses the wifi. So we would like to know how such huge amounts of data are disappearing? Went into Telkom Liberty Mall on 20 May, no feedback yet. We would like to know whats going on?