I find that Call Valet blocks up to 200 numbers, including all numbers from
a given area code - like all 800's. A bit pricey, but well worth it for me.
I had a missed call. When called back, it just disconnected.
I made an entry "SCAM" in my contacts and I just add all the sketchy phone numbers there, so I don't pick up when they call again.
I'm on the Canadian national do not call list and yet the technology is getting ahead of it.