Ok then what has happened is:
You bought an app - you own the app.
You removed it
you then bought some more apps, some of which aren't paid for yet - but you have got them.
before you can DL more content you will need to pay for those newer apps.
i think - correct me if that doesn't fit
You don't pay for apps immediately, as most buy a few in one visit they hold off the payments and then group them into fewer invoices. It saves them loads on card handling.