Blocked number called my iPhone?

This blocked number just called me. I know for a fact that I haven't blocked anyone. If I have someone else has done it. They called about four times and left a voicemail. I'm afraid to listen to it. What could this be?

Its probably one of your friends prank calling you, the number appears blocked on your phone because the caller entered *67 and then you phone number when dailing you. I did this to some of my friends when I was younger as well as them doing it to me.

Could've been a glitch. You should listen to the voice mail then you might remember you did block the number or if it is serious then you can report it to the police.