Contacts Block a number and unknown callers before being called
Open "Contacts" app : - tap on , - tap on "Settings", - tap on "Blocked numbers" (down the screen), - tap on "ADD A NUMBER", - enter a phone number,* - tap on "BLOCK". You can also block unknowned callers who don't belong to your contacts list.
* Calls are automatically redirected to the voicemail without notification. SMS/MMS are not received either. To unblock a contact, do the reverse setting.