Did you activate roaming on your account before leaving the UK?
(Pay monthly customers need to have been with Virgin Mobile for more than 3 months to do so).
If you didn't, log into your Virgin Mobile account then click on the "Plan and device" tab.
Go to "Manage my services" > "Roaming" needs to be set to ON & "International call barring" needs to be set to OFF.
If they are not already, make the change by moving the "switch/tab" in your account.
If you have to make a change to the settings, allow time for your account to update.(Virgin advise that this may take upto 24 or longer from abroad).
I would periodically turn the phone off/on to see if it finds and selects a network.
You may have to go into the phone's settings and "manually search for network".If roaming was already active, have you tried this? If it finds any, try selecting them.
If you want to say thanks > click 'Kudos'.Answered your question? > click 'Mark as Helpful Answer' also.