I need to know If there are some rail service from London to Brussels on Boxing Day. I´d like to get more info about that
Yes, on 26 December 2017 there are Eurostar trains running.
You can already buy tickets on the Eurostar website.
There is a Live Chat option on the site, so you can ask your questions if you do not want to believe the online information.
As the time tables change early in December I could not double check for you.
(The Eurostar site only gave afternoon and evening departures, which might well be true for the day but would be unusual for a normal day of service.)