school management

i want to use cron jjob to send sms for students after register in a course unless they have paid for that course.
using
wp_next_scheduled( )
wp_schedule_event( );
$timestamp = wp_next_scheduled( );
wp_unschedule_event( );
add_action();
and loop through all students
but not exactly process.

The School Management – Education & Learning Management.

thanks.