If you subscription is currently expired, you should be able to renew by going to http://billing.microsoft.com and signing in with the LiveID for your subscription, selecting Renew from the OneCare entry on your list of subscribed services, and then selecting to use a retail PIN/Key/Token. Removing the expired credit card should not be needed.
Alternatively, it may just be easier to uninstall OneCare and reinstall it from http://onecare.live.com and then activate with a *new* LiveID and your retail product key, abandoning the old LiveID and Billing account.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
If you post your support case number, I'll ask for it to be looked into for why you weren't called as promised.
-steve