17-09-2015 00:02 - edited 17-09-2015 00:06
There should be absolutely no one connecting to your phone or internet except you?
Have you had excessive usage and a high bill? You can check what you have used via MyO2
Are you by any chance on a shared data tariff?
We need more information before we can give you correct advice
on 17-09-2015 07:30
OnePlus 6 (O2 & Sfr), Z3 Tablet (Three UK), iPhone 8+ (EE)