Yes, OneCare is automatically renewed if your credit card and payment information is on file. You can check that information and also read the terms of service by signing in at http://billing.microsoft.com and selecting the OneCare subscription shown.
A notice regarding the renewal was sent to the the LiveID email address on file for that Billing account. So, if you created a new LiveID when you subscribed and got an @live or @hotmail LiveID, but didn't activate the associated email account (which is optional) your notice may have been send to an address that doesn't exist.
-steve