How to Block or Unblock WhatsApp Contact in iPhone, iPad: iOS 8/7
Open WhatsApp, and Open WhatsApp Setting.
Under the setting option Tap on Blocked tab add new browse your Whatsapp contacts and select the user you want to block and tab block Done.
To Unblock a user
WhatsApp app > Setting > Blocked Option
you can see all blocked contacts > To unblock Tap on red “Unblock” Button.