A quick search of the Community will show you are not alone.
If you are trying via the App then
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.
