In the dialer app, view the call log or contacts, select the call, add it to the "blocked/rejected number" list. (See the 3-dot menu if there is no button.)
Now the calls from that number will go directly to voicemail.
Otherwise,
Which phone?
Which version of android?
Which carrier?
phone-- samsungj7
version-6.0.1
kitkat
i am using you talk setting.. than block successfully .. but another person calling me.. then my phone is say .. busy.. this is my big problem.. i want block incoming call but say not busy