You can't block more than 12 numbers from Comcast. Even unknown and no number call can get though.
They say that political and charity can get though on a unknown number. You can't block international numbers, no numbers, spoofed, and a lot of other numbers, because Comcast won't listen to its customers and change the way they do their phone works. It's not like they can't, but because of money they won't.
I just got a call blocker, and it does everything that Comcast does not do, and will block up to 80 numbers.
The only thing is it cost $99, but it's worth it to keep my phone from ringing with all this stuff.