I try to add an email it says 'email already exists'

I try to add an email it says 'email already exists'

I tried to add an email name to my custom email domain hosting. When I try to add the email I need it says 'email already exists'. Then I try to find it under existing emails. I only find my first email 'nils@elprior.com'. I try to add 'support@elprior.com' but I can find the already existing one.

I try to delete 'support@elprior.com' but it's just not there..