Unfortunately this case is too frequent in the last year. I'm afraid that most of the times the only think you can do, if you're sure it's the manager's fault, who scammed the participants, is to give him negative trust and open a thread explaining your reasons.

In most of the cases, the members of the forum maintains their anonymity so it will be difficult for you to start legal actions against the shady managers, but you could try and depending on the jurisdictions they could end suffering the legal consequences of their actions.

I hope it helped. Let us know how the story ended. Cheers.