You don't say what Avast program you are using Avast Free, Premium, etc. ?
If a paid version of avast didn't you setup an automatic payment instruction ?
If not, then you should have got on-screen reminders of X weeks/days remaining, etc.
If so, you should have received a notification that payment would be taken in X days, etc.
The captcha is an anti spam measure and is only for your first 3 posts.