Legal action seems too complicated and expensive. If their promotional power is using advertising services outside of forums, then it's good to start reporting that to ad providers. In the end, the bad experiences of users written on various review sites will knock more into public awareness that this casino isn't worth playing.
I have also noticed how 1xbit advertise themselves on reputable crypto webpages, last time I checked some news web I liked I realized they decided to advertise it by publishing a "tutorial" on how bet on the casino. I felt disappointed and never read that web again.
I take for granted those web operators do not even know what they are promoting and (even worse) do not care enough to do a simple research before advertising. Because of it, I am not sure how effective would be to alert ad providers about this, they probably prefer to pocket the money and not to ask many questions.