I am getting constant calls from a number that shows up as "unavailable 000-000-0000." I imagine this is some kind of caller ID spoof or else is coming from a VoiP phone. When I try to block this number (including with an added "1" as a prefix) I get a message telling me to please enter a valid phone number. I already have anonymous calls blocked but this gets around that service. Anyone have any ideas on how to block these calls? Driving me crazy...