Several years ago Apple transitioned to using to two factor authentication instead of security questions. You can continue to use security questions if you already use them and they are working for you, but if you have problems then they no longer get direct support. You can try the directions in this support article If you forgot the answers to your Apple ID security questions - Apple Support but the article is labeled "archived" and may contain information that is out of date. If the instructions work then fine; if they do not (e.g., “not enough information”) then you will have to change to the newer security method if you can. Over the past few years Apple has been repeatedly and persistently encouraging users to switch to the newer security system. For those who have ignored their encouraging, Apple will likely only help you do that if you can. Follow the instructions in the "Turn on two-factor authentication for your Apple ID" section in this support article --> Two-factor authentication for Apple ID - Apple Support to try to change to two factor authentication.
If you still need help, contact Apple ID support at this link ➞ https://getsupport.apple.com/?caller=cups&PGF=PGF63005
Select "Other Apple ID Topics", then "Security concerns or account compromised." This will give you a chat or telephone call option.
If Apple cannot 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.
Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. Do this online at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not detail what currently constitutes proof. Prior to this service being offered officially and moved online, Apple typically required the original receipt issued by Apple or an Apple Authorized Reseller. If Apple resets the device this will give you access to the device but won't restore access to the account used to lock it. There is nothing that can be done to expedite an Activation Lock request.
Apple recommends you "Keep your receipt after you buy an Apple device" --> Keep your receipt after you buy an Apple device - Apple Support
Good luck!
