Comcast call blocking is a joke. If you want to block more than 12 numbers, international, no numbers, and much more, you need to check out call blockers that you hook up to your phone or if you leave your computer on 24/7, you can download programs that will block all calls. The Do Not Call List is also a joke, that doesn't work. I just got my blocker and it does everthing that Comcast won't do.
Good luck.