I am getting an error message when trying to add alias into outlook.com account

I originally attempted to use my custom domain with Outlook.com however decided it would not work correctly. So I backed out and deleted my Outlook.com admin account and domain setup. When I did this it stated the email name(s) would remain active without any email services. I then went on to create a separate email account with just the regular *** Email address is removed for privacy *** with no problem. Now when I attempt to use my email name as an alias under my new Outlook.com account it states "This email address is already taken. Please try another".
I have also tried to log into the account on both the Outlook admin and the regular account logon with the username and it states the email address doesn't exist. How do I solve this issue?