log into your account > click on the "Plan and device" tab.
Go to "Manage my services" > check that "Roaming" is set to ON & "International call barring" is set to OFF
This may be your problem. If so allow time for your account to update then reboot your phone by turning it off & on again.
You may also need to manually search for a network in the phone's settings.
If you want to say thanks > click 'Kudos'.Answered your question? > click 'Mark as Helpful Answer' also.
Thank you, problem solved.
P.S. would like to award a Kudos but the link didn' t work
glad I was able to help