Hello,
Is it one of these emails? outlook.com hotmail.com live.com msn.com
If so, it means the email address has been deleted, either by you as user error, or by someone else. The email address is unfortunately gone.
Microsoft doesn't reuse its own email address, so it cannot be added to created as alias for another Microsoft account. This is why when you tried to recreate, it says it already existed.
Microsoft explains it here: https://support.microsoft.com/office/add-or-remove-an-email-alias-in-outlook-com-459b1989-356d-40fa-a689-8f285b13f1f2 Under the section "Remove an email address", it says: "Are you sure? If you remove an alias that's an email address from a Microsoft domain (like @hotmail.com, @live.com, @outlook.com, or @msn.com), you're permanently deleting the alias and it can't be associated with any Microsoft account again."