Lots of problems since O2 made a mess of upgrading their systems
If you are trying to log in to the My O2 app
Instead try the web version
https://accounts.o2.co.uk/signin
If that works then delete the app, reboot phone and reinstall
If none of that works then
You can call O2 on 202
Or use the social media links below
Message them on Social Media. Facebook (https://o2uk.co/O2CFB) , Twitter (https://o2uk.co/O2CTW) or Instagram (https://o2uk.co/O2CIG)
This is not O2 and we are all customers here similar to yourself and cannot answer account type queries.
