Did you not set up roaming before you left the UK?
If you cannot set this up manually via your online account, then you will need to call EE on another phone or land line on +44 (0) 7953 966 250. If you are a pay monthly customer you can use the live chat function via your online account or via EE contract page. ( click on the cross next to EE and the live chat function will be visible).
If you have roaming activated then make sure it's activated on your phone under settings. If you have an iPhone try resetting your network under settings.
To contact EE Customer Services dial 150 From your EE mobile or 07953 966 250 from any other phone.
EE standard opening hours are 8am to 9pm weekday, 8am to 8pm on weekends.