Is this on the Web https://accounts.o2.co.uk/signin
or the App?
If the App delete it, reboot your phone then download it again.
Otherwise you will have to call 02 on 202 from your handset or
Message O2 on
(Facebook) (https://o2uk.co/O2CFB)
X (Twitter) (https://o2uk.co/O2CTW) or
Instagram (https://o2uk.co/O2CIG) ,,
They should be able to help you.
This is not O2 and we are all customers here similar to yourself and cannot answer account type queries.
