Welcome to the community and thanks for posting. I'm sorry to hear you can't connect to a network abroad.
You'll need to check whether roaming is enabled on your account. If you're on pay monthly this is automatically switched off to avoid any unwanted charges.
You can now enable this via your online account. Please click here to log in and follow these steps:-
Online account > Plan and device > Manage services > Going abroad
You can also check costs of calls, texts and reception here.
Hope this helps. Please let me know how it goes.