"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", read this link:
Security and your Apple ID - https://support.apple.com/HT201303
"Without proof of your identity ... and other carefully selected criteria(1), Apple Support can't help you perform any actions on your account." If you are still using security questions (see below) then you knowing your security question answers is the exclusive way, apart from potentially "other carefully selected criteria", of proving to Apple that you are the owner of that account.
(1) E.g., "In certain cases, Apple might also use your payment information to help verify your identity. You might need to verify your payment information to reset your Apple ID password" - https://support.apple.com/HT208683
It may ultimately prove very difficult to find satisfactory resolution to forgotten security questions if you get the "not sufficient information" message (e.g., https://discussions.apple.com/thread/252410816 ). For quite some time now Apple has been very strongly urging users to use Two Factor Authentication instead of security questions. --> https://support.apple.com/HT204915 "With two-factor authentication, you don't need to remember any security questions. We verify your identity exclusively using your password and verification codes sent to your trusted devices and phone numbers. When you enroll in two-factor authentication, we keep your old security questions on file for two weeks in case you need to return your account to its previous security settings. After that, they're deleted."
Here are two methods that are relatively similar for possibly recovering from "not sufficient information" by signing up for Two Factor Authentication at this stage:
Post by a Community Specialist, click here --> https://discussions.apple.com/thread/252885215?answerId=255425124022#255425124022
'Solution to the forgotten Apple ID security questions" --> https://discussions.apple.com/thread/252575591
Apple does have "Account Recovery when you can’t reset your Apple ID password" ( https://support.apple.com/HT204921 ) which it specifies is available for "when you don’t have enough information to reset your password." However, it also states it is "if you use two-factor authentication" which you may not be if you are still using security questions. You can investigate if this is even available to you.
With that in consideration you can try to "Contact Apple for help with Apple ID account security", click here --> https://support.apple.com/HT204169 If the online option does not resolve the problem I suggest trying to get a personalized response with a chat or telephone call. To talk by telephone: Contact Apple for support and service - Apple Support --> https://support.apple.com/HT201232
For other support options, including those if your country does not have telephone support, click here -->: https://support.apple.com/choose-country-region To chat, choose any topic, (not Apple ID) continue working your way down options until you find one with chat support, then ask to be redirected.
(Note: If your country is not listed, there may be a support option at the end of each region section for "other".)
