Hi,
What is your data allowance ?
Check in settings,mobile and look at the app list at the bottom. next to each will show how much data each App is using.
Use wifi when and where possible.
If on wifi and your iphone goes to sleep it will revert to mobile data so turn mobile data off when at home which will force it to stay on wifi or put it on charge and the same result will happen.
Settings, Mobile, Mobile data. {toggle to off but remember to toggle it back on to connect to 02's data service when out of range of wifi}
Also your apps will refresh in the background.
This is primarily a battery saving tips thread but some also save on data.
http://community.o2.co.uk/t5/Apple-iOS-Devices-iPhone-iPad/iOS-7-Battery-Saving-Tips/m-p/530730/high...
Tips link :http://www.thestar.com/business/personal_finance/spending_saving/2012/11/16/10_ways_to_cut_your_mobi...
If you feel after checking that the data being used does not reflect whats being shown on your iphone then contact o2 and question your data usage.
202 contract Customers.
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