You can cancel a lead from any channel you are integrated with directly through the Hostfully interface.
You must assign the lead to yourself in the dahsboard, if you haven't yet, to cancel the booking. If another teammate has the lead assigned, they must cancel the booking.
If the booking is populating because of an iCal, it needs to be removed from the site where the booking is actually made. If the booking is not removed, you will cancel it through Hostfully and it will reappear on your calendar since the reservation still lives in the actual booking channel.