First make sure that you have international voice roaming enabled and data roaming if you also got data in self-serve. They are free add-ons. After that restart your phone. If you still cannot get service then check you don't have roaming disabled in your phone and also look for automatic network type allowing you to connect to 3g/wcdma and 4g/lte. Then go select manual network selection and see what networks populate in the list after 1-2 minutes and see what It says as you try to connect to them. What phone do you have? Also may as well restart again.