I'm having trouble in the challenge for trailhead unit Controlling Access to the Organization
The challenge is 
" Your Developer Edition comes with a System Administrator user. Create a new user using the System Administrator profile and then deactivate that user to preserve the licenses in your org.
The new user must use the System Administrator Profile.
The username for the new user must include 'guestadmin' somewhere in it.
The new user must be inactive."

I created a new user with system administrator profile as required, but when I navigate to the users tab I do not see the created user.
The visible users are:


After reading another post for similar issue i tried to deactivate my already existing user with System Administrator profile, which I am unable to do.
Please guide how should I proceed in order to complete the challenge. Also is there any way through which all the users ever created be listed.

I'm unable to create a guest admin as part of the exercises in the Data Security module in Trailhead.  The license and related profile simply are not in dropdowns when adding new user,although the required sys admin profile actually exists in my developer edition.  How did people get around this? (PS - I'm in Data Security Module / Controlling Access to the Organization)