21-07-2019 09:37 - edited 21-07-2019 09:39
Check out the network status first https://status.o2.co.uk/ This will give you an idea if there is a problem with a local mast.
Other info to look at here https://community.o2.co.uk/t5/How-to-Guides/How-can-I-sort-out-my-network-issues/ba-p/1014088
Or download the My Network app https://www.o2.co.uk/apps/my-network
You could also remove the sim, gently clean it, reinsert and reboot the phone.
Hope this helps and welcome to the forum
on 21-07-2019 09:40
Firstly try simply turning phone off and back on again.
Also try removing and reinserting your sim.
If you can, try your sim in another phone.
If sim is faulty, any o2 shop will replace it free of charge.
OnePlus 6 (O2 & Sfr), Z3 Tablet (Three UK), iPhone 8+ (EE)
on 21-07-2019 18:34
This sounds like a sim card problem unless there is an issue with payments.