Please (re)search before posting.
Things you are asking are already answered many times.
1] Likely it is a auto-renewal that took place
2] avast sends you 3 emails before it takes place
3] No clue why you can't disable it, but everyone else can
4] There is a way to contact avast by mail, it is called a ticket
https://www.avast.com/faq.php?article=AVKB24Note:
It really is a very bad idea to mention your email on a (public) webboard.
Spammers and other bad guys will harvest it and (ab)use it.