There is no real way to track this except via the Audit Trail app where you could see the enrolment and unenrolment actions performed but not all the details. If you need to keep users in a session but show them as cancelled, consider 2 things...users cannot self-enrol into the same course but a different session concurrently; only a PU sir super admin can do that. If that’s ok with you, you could use one of the lesser-used statuses to act as a “:cancelled” status, like “suspended” or “overbooked”. Please test the  behaviour on the user end of using the “suspended” option as I believe it locks the course for the user.