Two mobiles both can only pick up 3G when should be able to get 4G/5G

[Sanders]

Two mobiles both can only pick up 3G when should be able to get 4G/5G

[Enlli]

One place or all over?

Contact of PAYG?

Try these guides

Guide: How can I sort out my network issues? 

Guide: Is the network down for me or everyone? 

[Sanders]

all over, everywhere. Contract. Cheers

[Enlli]

If the guides don't help you need to contact O2 by one of the methods below

Guide: How to find help & contact O2 

[japitts]

Does toggling flight mode revert the devices to the expected technology?

[Oxonian]

This might help @Sanders :-

My Network App - Find Out More About Your Network Coverage | Apps | O2

https://www.o2.co.uk/apps/my-network

Understand your network coverage

With the My Network app you can keep an eye on your coverage, wherever you are. Download the app and you’ll be able to:

- check the status of our network in your area – you don’t even need to enter your postcode
- test your network speeds
- report any issues with your service.

It’s simple to use and means that you can check the network without having to visit the main site or even enter a postcode.

It is mentioned in one of the guides already referenced ; it is well worth trying.