Unwanted blocked phone number

[Lonken]

I recently upgraded to an IPhone 5. Since that time I have not been able to receive calls from my sister. When she would call she would hear a single ring then sent to me voice message which I never get.
Today I checked my blocked list and her number was there. I have never blocked any numbers. Ever. How did this happen. Has this happened to anyone else??

 

[Applejuiced]

It doesn't happen on its own.
You or someone either did it by accident or blocked her on purpose without you knowing.

 

[MassiveAttack]

You blocked her. Just unblock her and problem is gone.