Just answered a call from this number. It was noisy in the background, people laughing etc and the guy said he was following up on my inquiry for United Health Insurance... I said I never inquired about insurance. He had my first and last name (which bothers me!) and said oh ok, I guess we have our records wrong. I just said uh huh and hung up.
Report these numbers to the FCC. Debt collectors are supposed to identify themselves. These are services they use to try to gather location information on you. Report them to the FCC and FTC if the numbers keep harassing you.