on 12-10-2020 14:22
on 12-10-2020 14:29
First check your network status here O2 Service Status
After that, it could be a faulty sim, faulty phone or account bar.
Try your sim in another phone, if it works your phone is faulty, if not, it's a sim or account issue.
You can get a new sim from any O2 store for free and call O2 to check your account.
Numbers here Guide: Coronavirus Community Help and Support