@aoifeglenn
You can try logging on at :-
https://mymobile.o2.co.uk/
If you are using the the app, try deleting it, rebooting your 'phone and then reinstalling the up to date version of the app.
However, that might not work. O2 have messed up a system update which is affecting many, many customers. If so, you will need to contact O2 as this is a customer to customer community with no access to accounts and no ability to help you directly. I suggest that you message O2 via social media :-
Facebook : https://o2uk.co/O2CFB
X (formerly know as Twitter) : https://o2uk.co/O2CTW
Instagram : https://o2uk.co/O2CIG
A schedule of how to contact O2 is in :-
Guide: How to find help & contact O2
