stop reminders from notifying a user when another user accepts appointments

Hi,

A UserA used to have UserB's calendar in his outlook so that he can manage the calendar.  That role has been passed to someone else but UserA still gets reminders when UserB accepts appointments.  Also, when UserB accepts appointments that was was sent to UserB by the new person, it still shows it as being sent from UserA.

- I ran get-mailboxpermission on UserB with the format-list option and I do not see UserA anywhere. how can I find out what permissions UserA has with UserB ?

This is in an Office 365 environment.

Thanks