I believe it is a debt collector. No messages left for me either, so it falls under harassment in my opinion. I believe a new MO for collector may be to call from numbers that are masked and directed to other area codes (for instance, a collector's office is based in a different area code, but the call is routed to appear as if it's coming from another place). It's legal for the collector to call until a certain point, so I feel as though this falls under a somewhat deceptive practice that hasn't been addressed in court.