Can’t receive or make calls while abroad

[ABS1]

I am unable to receive phone calls while I’m abroad. I can receive messages and SMS, internet works, but if someone calls me it goes straight into VM and I just get a message saying someone tried to call me. 
what can I do? 

[jonsie]

Try manually selecting another network

Refresh network settings

Change data APN to mobile.o2.co.uk

Reboot phone

[Enlli]

Check that 4G Calling is enabled.(Volte)

[pgn]

It would help to know which particular part of "abroad" you are visiting, @ABS1  - with 190 or so parts of it to choose from, not all parts offer the same opportunities or challenges to the O2 Customer abroad.  The Customer's service type is also a factor: PAYG vs.Contract, is good to know.

All of these insignificant, at first glance, details help us to help you: Guide: Roaming MegaGuide 

[ABS1]

You’re right @pgn 

its happened twice in Spain and another European country 

I’m on a pay as you go tariff

[ABS1]

For some reason I can’t find that option on my phone 😭

[Enlli]

Roaming in Europe is going to become more problematic in Europe as networks switch off 3G. 

Normally, PAYG phones make calls over 3G, switching down from 4G. If 3G isn't available then the phone should drop to 2G, but it doesn't always happen, or happen quick enough

Unless O2 turn on 4G Calling for PAYG then the problem will worsen