Thanks for your post on the Community and welcome. I'm sorry to hear that you are experiencing an issue with your roaming service. Did you verify that roaming was active before your trip (you can check this via your online account under Plan and Device > Manage My Services)? Also please make sure that International call barring is OFF.
Also, please try manually selecting the networks available to see if you can get a full working connection.
If your roaming hasn't been activated before leaving for your trip, we can try resetting this on the network, but please be aware that our reset may not work, as this depends on the local host network picking up the correct details from the UK.
If you are still having an issue with your roaming service and would like for me to check this, I will need to take more details. I will send you a private message requesting more information so that I can assist with this issue. Just click on the little plum envelope at the top right hand side of the page to access your inbox.