I block every single call like that if it doesn’t show up in my contacts and no message.
I’ve never actually blocked a call. I just don’t answer.
BTW, Our MY-Fi router at home broke so I used an old LG G3 as our main internet router in our home (we’re in the sticks. AT&T data plan is all we have). Since the phone has the capacity to receive calls, it gets a LOT of solicitor calls. But the ringer and vibrator are both off, so meh.
BTW, we use it to stream hi-def Amazon prime TV and movies. We live in the future. :)