I successfully charged back 6 months of WoW time via paypal on multiple accounts. Blizzard does not dispute charges because it is not worth the money to do so. The thing is that you paid for it, and it was not delivered. I would suggest contacting WoW asking for a prorated refund. If they do not give it to you, then do a charge back via paypal. State that you tried to contact the company, give logs etc. It is a sure win in your favor since they will not contest it.
Another angle is to tell paypal you forgot about the recurring charge and have not used the service in x amount of months. They will refund that too.
Lastly you can say it was an unauthorized charge, except the burden is more on you for that.