Make sure you have data roaming turned on.
Turn phone off and back again after.
Try a manual network selection and choose a different network to the one you are connected to now.
Also, are you contract or PAYG?
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion.
This is not Customer Service so we are unable to help with account specific issues.Currently using:
Pixel 7a (O2 & Lyca), One Plus 6 (Sfr), iPhone 12 Pro Max (Vodafone)