To protect your invention, you must apply for a patent. If your idea was stolen and you told this prospective company about an idea without actually writing that idea down, naming it, or acquiring a patent on it (if it's an invention), then you are likely out of luck. But maybe addressing a lawyer is worth it (if you are in search, I can recommend talking to the lawyers from https://zamani-law.com/, I had a great experience with them). I personally would consult a specialist.