MagiCall is a very powerfull program with so many feature, and it will "block" or do what ever you want when setting up the rules.
I have MagiCall and it does block "unknown/private" call, I set up a rule to "pick and drop" when "unknown/private" so when they call the phone will of course pick and drop and will not even ring, also this option will not let the other party leave a voicemail since the phone answered and hungup. I love this option
Give the trial version a try...you will like it...it is worth every penny...
You can also set modes or rules...like mute..etc...I have mine set to mute SMS from 2200 to 0800 M-F.