I just have a contact saved as "block", I add any unwanted numbers to that contact. I have gone into that contact, edited it and set the option to send all calls to voicemail. My phone has rung A LOT less since I did that. Someone had given my number on some financial aid application or something, the calls wouldn't stop even when I told them they had the wrong guy. If I answered the phone with my name ("name speaking") they'd just hang up when they realized they had the wrong number. When I made that contact and set it that way, the calls diminished as the numbers added up. I did this on my Moto X running KitKat and the send to voicemail setting carried over with the contact when I set up my 6P.