Before you left to go abroad did you check that roaming was active on your account?
Have you tried doing a manual search for network since arriving?
Log into your Virgin Mobile account then click on the "Plan and device" tab.
Go to "Manage my services" > "Roaming" needs to be ON & "International call barring" needs to be OFF.
If they are not already, make the change by moving the "switch" in your account.(Click the other side of the rectangle box).
If you have to make a change to the settings, allow time for your account to update then reboot your phone.
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.
Here is a useful help page from Virgin: Taking your mobile abroad
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