500mb depleted on mobile phone in one night

Yesterday when i check data balance around 19:00 my data were 1040, I use personal to check my gmail , Facebook on opera mini, chat only on Whats App and google i don't updates apps and watch videos.I have disable internet access on my phone to all apps except Whats app and Opera mini.<br> <br> I normally bought 250mb and it can still last for 2 weeks when am using it on PC even when i left data active.<br> Today when i wake up i open google and search some websites without watching videos , i only download 1mb file but when i check the balance it was 489mb. <br> <br> I called 081 180 to demand answers regarding this data usage but i was told that is because the data were left active.<br> I bought 2gb data last month but i was leaving data active but i never experience such data usage.