First this is not a thread on why to unsub, or even if it is a good idea. It's just I noticed recently a large number of posts by people wanting to refund Warlords over the recent turn of events, and they unsure as how to do it.
So here is the easy guide.
Log into http://us.battle.net/wow/en/ by now you should have it bookmarked. p.s. if you are not in North America it wont be us.battle.net so make sure to use your book mark and not the link.
Choose Knowledge Center
World of Warcraft
"I have an issue with a purchase or payment"
"I want a Refund for a purchase I have made"
"I want a refund of a copy of World of Warcraft I have purchased through Blizzard"
Last part I can help you with, you have a choice here.
Any of these choices work, however personally I just submit a ticket, asking for the refund and the reason why. Although if you are willing to wait with your phone, or on the page the other two options will get results faster.
Thank you for your time, and be sure to inform anyone unsure of how to get a refund by using my handy guide.