Welcome to the community and thanks for posting.
I'm really sorry to hear you're not able to use your phone abroad. I'd really like to help with this. Would you be able to reset it via your online account?
Please turn roaming off. A green message will appear. You'll need to wait 2-24 hours for this to be successful. Then you repeat the process to turn it back on again waiting a further 2-24 hours.
After this has been done and shows as active again please restart the handset to see if it now connects to a network.
If this fails, and you can get to a phone, then please call our team on +447953967967 as there may be another issue.
Please let me know how you get on with this.