Impossible to add existing user?

Impossible to add existing user?

I started to set up mail under my own domain.  I added some users and then ran in to problems so I deleted the entire organisation and started again.

The problem is when I try to create the same user now I can't as "they already exist".  I therefore invite the user again:
http://note.io/1ctZca1

When I do this nothing happens.  No emails are sent etc.

If I try and login as the user and delete their account I can't because I get an error saying they are admins of the organisation I created and I should remove them first.  I can't do this as they are pending users now and not admins:
http://note.io/13bJrpT

Why is it not possible to delete this user or re-add them to the control panel?