We have the same issue with Moodle 3.6. Suspended enrolment status doesn't seem to have any effect on the student.
I tested on https://school.demo.moodle.net (running 3.7) and had the same issue.
On https://qa.moodle.net/ (latest 3.8 today), it works as expected.
It must be a matter of version. I didn't find anything in the tracker regarding this issue.