It is pretty likely that you will not be able to recover you account at this stage unless the people who stole your account were pretty stupid and left some of your personal information on it such as your telephone number.
Read this document if you think your Apple Account has been compromised. --> If you think your Apple Account has been compromised - Apple Support
For iOS 15 or earlier, if you want to see if anyone else has access to your device or accounts, click here --> Checklist 1: Limit device and account access - Apple Support
For iOS 16 or later see how Safety Check on iPhone works to keep you safe. Safety Check for an iPhone with iOS 16 or later - Apple Support
Use the information in this document to check your Apple ID device list to find where you're signed in --> Check your Apple Account device list to find where you’re signed in - Apple Support
Related materials:
Personal Safety User Guide
Personal Safety User Guide - Apple Support
> open the Table of Contents and review the articles
A document with general information about security and your Apple ID --> Security and your Apple Account - Apple Support
Contact Apple for help with Apple ID account security. This page provides country-specific Apple Support contact information ➞ Contact Apple Support - Apple Support
As for that message, several years ago Apple transitioned to using two factor authentication instead of security questions. Over the past few years Apple has been persistently encouraging users to switch to the newer two factor authentication security system. For those who have disregarded their encouraging, Apple will likely only help you to now change to two factor authentication, if even that is possible. Follow the instructions in the "Turn on two-factor authentication for your Apple ID" section in this support article --> Two-factor authentication for Apple Account - Apple Support to try to change to two factor authentication.
If you still need help, contact Apple Account support at this link ➞ https://getsupport.apple.com/?caller=cups&PGF=PGF63005
Select "Other Apple Account Topics", then "Security concerns or account compromised." This will give you a chat or telephone call option.
If Apple cannot, or will not, help you transition to two factor authentication then it is quite possible you will have to simply abandon the old account and everything it contained. In that case, if you were using the Find My service, the Activation Lock support request support article at: - https://al-support.apple.com/#/additional-support may at least let you regain use of your equipment. If not, you will also have to say goodbye to the device as well.
Good luck!
