Hi Bren1,
You can see your data breakdown on certain phone models. What phone are you using?
For peace of mind, if you have wifi available it might be worth switching off mobile data temporarily and using wifi to preserve your data.
Failing that, you can book an appointment online with one of our gurus in store and they will be happy to help you find out what's using your data. Head to
https://guru.secure.force.com/O2DeskStoreLocator to book an appointment.
