You your account no longer exists in Battle.Net and you get the "Account not found" error message, it means there is no account with your email anymore.
Hacked or Compromised
If you've given your account information to any friend, they might have changed the email to something else.
In this case your only option is to create a ticket [https://eu.battle.net/support/en/help/product/services/316/979/solution] in Battle.Net and provide as much information about your account as possible.
- Alternately you can try restoring your account using this link https://eu.battle.net/support/en/help/verification?stateRef=%2Fsupport%2Fen%2Fhelp%2Fproduct%2Fservices%2F316%2F979%2Fsolution