Unfortunately you are screwed. I've had this happen to me twice. Once in Spain and once in the US. You have to inform virgin before you travel that you are going abroad and ask them to allow roaming. It's absolutely ridiculous. Don't expect any help, sympathy or compensation. And don't think that just because it happens once it won't happen again, because it will. Unless you tell them. Every time.
If you have saved offline maps on google, they won't work either.
Try and enjoy your holiday, you have a brick that only works with wifi.