Don't listen to the people here telling you to just "move on". You worked for half a year without salary; they don't get to screw you and get away with it. There is no "high road" that benefits exclusively them.

Get a lawyer now, do not sign anything, do not pass Go. Upvoted advice in the other thread applies. The card you hold is the threat of a lawsuit, which happens to be justified.

To be clear: you're still an idiot. They're jerks. Let this be a watershed moment for you.