Can't add users... Already in use.

Can't add users... Already in use.

Hi I cannot add the following users because they are already in use :( I'm trying to add a new domain but it says these emails are already in use

holden@autocarcredit.com
sam@autocarcredit.com

I think they may have been used as a secondary email for other domains in the past but I own autocarcredit.com and want to use those domains under my account. Thanks