Your account is easier to hack the more people you share the log-in information, so the best way to fix it is to reset your password and consider limiting access for others.
After changing your password, go to the “My Account” page and click “Sign out of all devices” under the settings heading.
That will kick all the people that have been using your account off. Just share the new password with your family and/or friends--perhaps in person or over a secure email.
Fortunately, Netflix obscures user’s credit card info, so that should be safe. If you’ve been using your Netflix password for other websites, though, make sure to change those, too.