iClosed allows you to prevent users to reschedule calls and here's how to set it up:
Navigate to
AI Scheduler → Events pageLocate Event you would like to disallow rescheduling of the events
Click on the Event to open Event Builder
Navigate to "Event Time & Limits" section
Head to the "Allow closers to reschedule this event" toggle button
Turn OFF to disallow event rescheduling
Or turn ON if you would like to allow Hosts to be able to reschedule event
Learn more about Scheduled calls and all features in it here.