You really need to be careful about how you approach this sort of issue. While the advice may be trite, it is particularly apt here to emphasize the importance

You really need to be careful about how you approach this sort of issue. While the advice may be trite, it is particularly apt here to emphasize the importance of consulting with a lawyer who is strong on IP issues. In particular, this would normally need a careful evaluation of the contract language, which may or may not define what happens in the particular case you describe. If it should not adequately define what happens in express contract language, then there are default rules that potentially govern what happens. Those rules may or may not support your position. I have bumped into cases where the default rules basically say that the contract assigns the IP rights to the customer regardless of non-payment, with the remedy for the developer simply being to sue for payment. I am not saying that such rules govern your case because it is not possible for anyone to really know your case absent a proper legal review by a knowledgeable lawyer. I am saying you may be making assumptions about your legal rights that may or may not be correct and you should not casually just assume that they are. It goes without saying as well that you should be cautious about using pejorative language about the person who did this in public because of the obvious risk of setting yourself up for a defamation claim. Again, in the end you may be justified but why complicate your own claims by giving those who did whatever these people did free ammunition to fight you with. I don't mean to sound unsympathetic. It hurts to get screwed and it sounds like that happened here. Just be careful to go about it the right way in trying to correct the wrong that did occur.