I would walk away. Actually, consider yourself lucky that they've shown their true face so early on and you can get out now :-)
When considering hiring a lawyer etc., also take a look at opportunity cost: Even in the best case scenario, will you get more money out of it then if you freelance for a similar amount of time? Probably not...
(Also, learning from the Winklevoss twins, it seems preferable to sue a company when it is actually successful, because they got way more to loose at that point then now. Although I strongly doubt that they'll be successful...)
When considering hiring a lawyer etc., also take a look at opportunity cost: Even in the best case scenario, will you get more money out of it then if you freelance for a similar amount of time? Probably not...
(Also, learning from the Winklevoss twins, it seems preferable to sue a company when it is actually successful, because they got way more to loose at that point then now. Although I strongly doubt that they'll be successful...)