Users being Deleted on completion of course

[gerodea]

My users are enrolling into Groups using the enrol key authorisation, with Group Enrolment Keys.
This is working successfully, and the Enrolment duration is set to 300 days.
Unenrol inactive is set to "Never"

However, it appears that users are being deleted from the system (with no trace) once they complete the course.

My local tech support has diagnosed the following:
_"The user account is tied to the enrolment on the course (Their authentication type is set to enrolkey) so when the enrolment ends their account is removed. You will ned to use a different authentication type for your users (manual or email based probably) which removes the connection from the user's account to the enrolment of the course."

"Unless there is an option causing the user to be unenrolled on course completion that would trigger the deletion of the user I'm not sure what the issue would be."_

Can anyone help please?