Apple id

"If you see a message that the email address you want to use isn't available or is already in use, check that you or a family member aren't already using that email address with a different Apple ID. If a family member is using that email address, remove it from their account then try to use it." From: Change your Apple ID - Apple Support

Although this next section discusses email address re-use in the context of deleting an account, it supports observations frequently posted on this forum about not being able to re-use an email address as an Apple ID once used previously as an Apple ID:

From: How to delete your Apple ID account - Apple Support

"Can I use the primary email address for my deleted Apple ID account to create a new Apple ID or with another existing Apple ID account?

No, once your Apple ID is deleted, you can't use the email address that you used with it to create a new Apple ID. In addition, you can't use that email address with another existing Apple ID except as a rescue [notification] email. Also, if your primary Apple ID email address is with a Custom Email Domain, it can never be reused to create an Apple ID after your Apple ID is deleted, even if the domain ownership changes."

If you still have questions or problems:

Refer to this document for ways to contact Apple --> Choose your country or region - Official Apple Support

Select your country (also look for "other" regions), then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.

or:

Contact Apple for support and service by telephone --> Contact Apple for support and service - Apple Support

If you get a message about not having 'sufficient information', you will not be able to reset your security questions.* Realize that several years ago Apple transitioned to using to two factor authentication instead of security questions and has been encouraging users to switch to the newer security system. Your next recourse will be try to change to two factor authentication as outlined in this article --> Two-factor authentication for Apple ID - Apple Support Follow the instructions in the section "Turn on two-factor authentication for your Apple ID"

If you wish to speak with Apple about this, contact with Apple ID account security using the information in this document --> Contact Apple for help with Apple ID account security - Apple Support

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*Dec. 2022 post by Apple Community Specialist K_Faith in the thread I’ve tried resetting my security question… - Apple Community

"If you’ve forgotten your security questions, there isn’t a way for Apple to reset them for you, or another way to access your account. You would need to create a new Apple ID, which also means you won’t have access to previous purchases or data stored in iCloud."