I used skype on my iPad and I got some unwanted call even though the contact I have already blocked.

I just noticed that I didn’t set good privacy but I can’t find the settings directly on my iPad3.

Indeed, we need to go to skype on PC and set the privacy settings (Tools -> Options) completely all to:

people in my Contact list only

(by default, it accepted call from anyone!)

So don’t forget this settings if you are using skype on iPad or similar devices that cannot see privacy setting there.