No phone signal or mobile data abroad (Europe)

[Lmc1]

For several years I have had no phone signal or mobile data whenever I am in Europe. When I turn my phone on initially it gets one bar of signal for about a minute and then it drops off, and I am entirely reliant on WiFi. 
I have had many conversations with 02 on the phone and in store regarding this to no solution. 
I have an iPhone 13. 
Things I have tried:

Toggling airplane mode on/off

Manually selecting networks (various network options come up but none give me any signal at all) 

Turning the phone on and off again 

Changing my data apn to mobile.o2.co.uk

Dropping my data option down to 4G

At one stage I thought it might be the phone itself but the problem persisted when I got a new phone. 

None of the above options have worked, speaking to 02 about it hasn’t worked. I don’t have a basic phone signal and I’m at a loss. Any help?

[MI5]

@Lmc1 

If you have roaming enabled in your settings, it can only be a roaming bar on your acount.

You need to contact O2.
Message them on Social Media. Facebook (https://o2uk.co/O2CFB) , Twitter (https://o2uk.co/O2CTW) or Instagram (https://o2uk.co/O2CIG) or give them a call on 202 or 0344 809 0202 (contract) 4445 or 0344 8090222 (PAYG)

Guide: How to find help & contact O2