It could be a fault that CS aren't aware of so it would be worth you calling to report it.
You can also try a sim swap - just pop into any o2 store and they will change it for you for free.
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)