My account was hacked by an unknown person.

Hello!
My Gmail account was hacked by an unknown person and it's connected in Clash of Clans, and there is a new update, when I had finished it from updating, when I log in, the game restart, I came back from th7 to th1, so I had signed up again my Google account ***@*** but when I input my password: namikazeminato, Google says:your password was changed 9 days ago, but i didn't ever changed my password, I think it was opened by an hacker and the hacker changed my password, so please, help me!