A warm welcome to this O2 customer to customer community @jade091016.
If you are trying to access MyO2 using the app, try deleting the app, rebooting your 'phone and then reinstalling the app.
Alternatively, you can try online using an incognito or InPrivate tab in your browser to get to either :-
https://mymobile.o2.co.uk/
https://accounts.o2.co.uk/signin
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