Why was a client able to schedule a meeting over an already made appointment in my calendar?
If you are noticing others are scheduling appointments/meetings over your already scheduled ones in your calendar you will want to make sure you don’t have your appointments marked “Tentative.” If your meetings/appointments are marked “Tentative” it will allow others to be able to schedule over it. So to prevent this be sure to go in and uncheck this and/or make sure it is unchecked when you are creating the appointment/meeting.