Duplicate email addresses

After thoroughly deleting an email group for the art tour that I’m on as I am going to add them back in plus some new ones I keep getting the message that that is an existing contact. It is not! And I’ve searched all through my email lists, and it tells me that I don’t have a contact under those names so I cannot create them as a new contact or add them to a list . Can’t seem to figure out how to fix this or what to do. Any help is greatly appreciated! Thank you. Dawn