Delete Student Accounts

When I delete students from a course or all courses, it appears their accounts still exisit and new users can’t sign up with the same email ids. How do i permanently delete user accounts from the LMS?

I am using my testing email ids to test enrollment in courses and want to remove them to be able to re-use for testing purposes, but when i delete them and then go to sign up again – it says account exisits with that email id (even though that email id does not show up on any of my courses’ students.

Please advise.