After you installed the trial for OneCare, it will suggest that you can subscribe with a link within the program. Activation and subscribing are one and the same. If you provided credit card information, you were subscribing. You also clicked through the subscription agreement which outlined the cost and terms of the subscription.
However, all is not lost. If you did not intend to subscribe, you can request a refund from support.
They will cancel the subscription and enter the refund, but your trial version will then expire and you'll need to reinstall, at which point I believe that you will only get a 15 day trial before you need to subscribe.
Be sure to discuss your options with the customer service rep -
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve
