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?
According to the Azure support it is (currently) not possible to delete canceled subscriptions.
Greetings from Microsoft Azure. I reviewed your request and would like to mention that there is unfortunately no option to remove the disabled subscription from the Azure portal. This is by design to enable customer’s view the subscriptions purchased by them right from the day the Azure account was created.
I consider this a bad design choice but that probably is just me.