In my Windows Azure Management Portal, I still see the "3-Month Free Trial" subscription although it has already expired and been canceled automatically. I've deleted both the hosted service in it and also the database, but it still doesn't disappear.
What can I do to completely remove a subscription?
Visit the portal. In the upper-right corner, you should see a link for Billing.
This will take you to a list of your subscriptions.
Select your subscription. Then, on the right side, you'll see a few options, and one toward the bottom should be 'Cancel Subscription.'