This might not be helpful to you, but Old-Guy messaged me the below and it worked for me.

If you've already claimed your account and see the message to claim it again or Discord says your email is already registered, follow these steps:

Log out of whatever account you're using on Discord
Go directly to the Discord login page
Log in with the email they are saying is registered
If step #3 fails, use the "lost password" link on the page to reset the password