Make sure you build a case, keep copies of any and all communications (emails, contracts) that you've had with this character and make sure you don't lose a thing.
A single email can make all the difference if this ever goes to court and it might be a while before you get there, ideally you'd have started building a case long ago, but now it is definitely time to get organized.
If you should go to court, the major advantage you will have if you are organized is that you can present your case in a way that someone can follow. A case is like a piece of software in that respect, if it looks like 'spaghetti' then you will have a hard time arguing it, if it is nicely structured with layers building upon other layers you will stand a better chance to come out ahead.
Good luck with this!