partsproduction,
avast didn't steel anything from you, it just did as you agreed to.
When purchasing a license you agreed to auto-renewal.
You could have chosen not to by simply removing the checkmark in front of it.
You also could have disabled it anytime you wanted, but you didn't.
Since you didn't disabled it, the automatic renewal will take place.
Several mails (3 iirc) where also send to you before the auto-renewal took place.
That gave you another chance to disable it, but you didn't.
A landlord will keep billing you if you don't tell him that you have moved out.