We have had quite a few reports of high data usage on Iphones recently.
Have you checked your phone to see what's using most of it?
You can also compare what your phone says against what it's saying in My O2 http://www.o2.co.uk/myo2
You could have a load of apps running in the background...
If you have WiFi assist on, you need to turn it off.
*The Game Is On*
Please note, this is not customer services and we cannot access your account. Do not publish personal details (email, phone number, bank account).
Link to our guide on how to contact them can be found here
We all know there is something badly wrong with the way O2 register data usage but they will never admit to it. Speak to customer service and a sympathetic adviser will probably reset your data or add a bolt on. Sadly that is all you can do other than making a complaint via email. You need to reset your own data use settings at the beginning of each cycle. It's easy to do in the phone settings and you can then have something to compare with the usage shown in My O2. If you have problems setting it then let us know and we can help you.
Track usage, upgrade and get support with the My O2 appDownload My O2