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 use to see their ads on one article site where I subscribed in, right now they are not showing the ads anymore but they are now concentrating on the forum signature campaign they have three campaigns right now, and I noticed they are attracting new accounts with no bad trust these new accounts prefer to have a tag because of the high payout rate, they have the money and they are using to platforms where they can advertise their casino.
All the gambling community can do is to report write reviews and testify with proof that this is a scam site and gamblers should stay away from this casino to protect their money.