By default there is no Recovery Contact set up. If you turned on Advanced Data Protection, you are required to have either a Recovery Contact or request a Recovery Key.
If you think your Apple Account has been compromised, then change the Password and follow the steps here:
If you think your Apple Account has been compromised - Apple Support
Also go to Settings > [name on top], and scroll to the bottom to see other devices that are signed into your Apple Account. Any device (iPhone/iPad/Mac) listed there can make changes to your Account and even add a Recovery Contact.
If your Passcode is known by anyone else and they have physical access to your device, they can add a Recovery Contact. In that case, you would also want to change your Passcode.