Not likely blocked but rather called by a dummy number to thwart chances of being traced. If you don't know the number, don't return calls whatever you do. It can cause you more problems than bring you good.
They have been Calling me at least once a day for a week now they only left one message but it sounded like a computer told them I answered because they the vuy just kept asking for me until he realized i didn't answer.
This number called and asked for a male's name not of this household. When I asked for a last name they said something incoherent. It was an American/local voice. If I weren't expecting another call within the area I would not have picked up.