I may be late to the party (if you already know this) but after getting loads of annoying sales calls recently, I have found an app for Android phones that blocks incoming numbers: Mr Number https://play.google.com/store/apps/details?id=com.mrnumber.blocker&hl=en_GB It is free and can give you the option to drop the call, or send to voicemail. Just tried it and it seems to work. It also claims to be able to block unknown or private numbers as well. +1 to getting my sanity back!
Just had a read online and if you have a Samsung phone it may have call blocking built in. Good find @SkutterBob .
