"If you forgot the answers to your Apple ID security questions" click here --> https://support.apple.com/HT201485
If you see the message "not sufficient information" see if at this stage you can still sign up for Two Factor Authentication. Apple has been very strongly urging users to use Two Factor Authentication instead of security questions. "With two-factor authentication, you don't need to remember any security questions.
Click on this link for more information about 'Two-factor authentication for Apple ID' --> https://support.apple.com/HT204915
If you cannot resolve the issue by signing up for Two Factor Authentication, "Contact Apple for help with Apple ID account security"; click here --> https://support.apple.com/HT204169