A warm welcome to this O2 customer to customer community @Smith0555.
It is not clear how you are trying to access MyO2, bit online you could try using an incognito or InPrivate tab in your browser to get to either :-
https://mymobile.o2.co.uk/
https://accounts.o2.co.uk/signin
If you are using the app, try deleting it, rebooting your 'phone and then reinstalling the app.
If that does not grant you access to MyO2, I suggest that you contact O2 via social media :-
Facebook : https://o2uk.co/O2CFB
X (previously known as Twitter) : https://o2uk.co/O2CTW
Instagram : https://o2uk.co/O2CIG
The social media team are based in the UK and have a good reputation for solving customer problems.
Please also see :-
Guide: Upgrading Your O2 Phone
You can upgrade by visiting your local O2 retail store :-
Store locator | O2 UK | Find Your Nearest O2 Store
https://stores.o2.co.uk/
