You can try contacting iTunes support via this page and see if they will refund or credit you : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then Purchases, Billing & Redemption
You might contact Customer Service and see if they can do anything for you. In the end, though, it was your fault for not realizing your subscription was on auto-renew.
Which subscription, by the way? iTunes Match? If so, they sent out an email about a month before the anniversary date informing you about the charge.