It seems plausible that they could have actually stolen your intellectual property, in which case you might have grounds for a successful lawsuit. If you could somehow acquire the course materials they are currently using, and compare them to the work you did for them, you could sue them for copyright infringement. Compare the course work they were using before your interview to their current coursework. You have a common law copyright for anything you write, even if it isn't registered. I'm not a Lawyer, but i think you might have a case.