Roaming can now be activated through your online account. Log in here and you'll be able to turn this on through Plan and Devices and manage services. I did this and was taken to a site that has no mention of Plan and Devices and manage services. Stuck in Italy with no phone cover please help.
If you're abroad and roaming isn't working at all for you, the same team will be able to look into it for you. They can be reached on +447953967967. The team can turn this on from their side. Once this has been done, give your phone a hard reboot (popping the battery out of the phone while it's turned on ) to allow the sim a connection refresh.
Might be your best bet to borrow a phone and call them