My icloud account was hacked, I changed the password, what else should I do?
Yes, if they activated "Keychain" using another device you should change your passwords.

Keep in mind that activating "Keychain" in the iCloud preferences should require you to confirm the device using another device.

Please check to see how your account's authentication is currently set up (e.g. log out of your Apple ID on your Mac (iCloud), turn on iCloud using your Apple ID and try to activate "Keychain". Now your Mac should prompt you to activate Keychain using on of your other devices.