Try online https://mymobile.o2.co.uk/
If using the app, try deleting, rebooting phone and then reinstall the app.
This is a customer to customer community, not O2.
You need to contact O2.
Message them on Social Media. Facebook (https://o2uk.co/O2CFB) , Twitter (https://o2uk.co/O2CTW) or Instagram (https://o2uk.co/O2CIG) or give them a call on 202 or 0344 809 0202 (contract) 4445 or 0344 8090222 (PAYG)
Unlikely that you'd get help in store, but may be worth a last resort try.
So many customers now having this problem
Try logging in the website
If you are able, uninstall the app, reboot the phone and reinstall
If still an issue
We’re just customers like you but it sounds like you’ll need someone to access your account which can’t be done from here. If you message O2 using the links below, they should be able to help you with this
or give them a call on 202 or 0344 809 0202