If you already have a subscription to OneCare, the LiveID will serve to link your installed copy to that subscription.
If it did not ask for payment information or a retail product key and you did not have to agree to a purchase contract, you already had a subscription on that LiveID.
Go to http://billing.microsoft.com and sign in to verify the status of your subscription, if you have one.
Open OneCare and click Help/About... to see the Subscription ID.
The special discounted price was available via a special URL. If you activated from within OneCare (and provided payment information, which you say you didn't do), you will be charged full retail price for your region.
-steve