I just found a movie for sale on Amazon.com.?

I just found a movie for sale on Amazon.com. It's from an indy film company that I shot a short horror film that I wrote with. The full length film they are selling looks like it is from a script I sent them and based on the horror character I created in the short. The problem is, I haven't heard from these people in over a year and a half. I had the script I sent them registered with WGA from before. What are my rights concerning this? What should I do about this?