How to reveal a blocked caller ID?

I've been receiving calls, from a blocked number through my iPhone 5 (iOS 6.0)
and they call me at 1:00 AM every night.
I was hoping someone could tell me how to reveal a blocked number so I can get to the bottom of this. I'm from Israel btw

Http://www.ehow.com/how_4494174_call-private-number-back.html

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