Have you tried turning it off & on again to make it search for a network?
Although you asked the team, log in to your account > click on the "Plan and device" tab.
Go to "Manage my services" and check that "Roaming" is ON & "International call barring" is OFF
If this was your problem and you have to change the setting. Allow time for your account to update then reboot your phone by turning it off & on again.
If you are still unable to use your phone you could try using the web chat option to speak to an advisor: Help and Support - Contact Us > Mobile > Mobile not working > Chat online.
The advisors are sometimes busy it may take a while to get connected.
Or perhaps you could borrow or use a pay phone to call Virgin Mobile UK support line: +447953 967 967
If you want to say thanks > click 'Kudos'.Answered your question? > click 'Mark as Helpful Answer' also.