When you have difficulties in connecting to a network abroad and the only thing that you see on your phone is 'No Service' then you may need to select the network manually, i.e the phone is not automatically connecting to a carrier.
To do this, open Settings, select Mobile Data and click on Network Selection:

Here you need to uncheck Automatic and allow the phone to search for possible carriers, then select from the list any carrier that appears. The phone should connect to that system.