Get legal advice, explain to the band that you are willing to take legal action, ask for your share back nicely(say it to the bassist first, to try and persuade them), if nothing comes out of that go medieval on their ass. Sue them, message the tour promoter, spread bad stuff about the band. No one wants to buy the music of dicks, tell people on metal forums etc whats happened, gonna tear down the bands reputation. Worst scenario, you don't get your money back, and they continue to do barely mediocre. Best scenario, you get your money back and they get booted off the tour with a huge dent to their egos, drummer mostly. Its dirty work but its only fair.