I work for Lone Star, a medical billing company. If you received a call, it means you have a bill from a doctor, and it IS legit. You cannot just say the word "fraud" without knowing what you're talking about. Did you even bother to call the number back?
Lone Star MSO is an accounting and billing company used by a lot of Doctors in the Dallas Area. I have called to get statuses and clarifications on my Neurologist's bill. They do call back and they do leave messages. I had no idea who they were when I was first contacted and was suspicious when I received a call. My doctor did confirm later who they were. I left caller type as unknown because none of the caller types matched the call.