Have a look at these previous articles on my blog.
http://barlaventostravelblog.blogspot.com/search?q=Porto+Vigo
Note the service offered
Also, if you go to my blog at:
http://barlaventostravelblog.blogspot.com
Scroll down on the right until you reach the panel entitled
Algarve & Portugal - Travel Transport Links
You will find a link entitled:
"Porto - Vigo Train Timetable (PDF)"
Click on it and you will be able to download the current timetable from Portuguese Railways.
You may find it better to use one of the cocah services operated by www.internorte.pt which operate via Porto Sa Carneiro Airport to Corunha.
Current Services and one way tariff as follows:(Click to enlarge)