I created a new event in my Google calendar and invited attendees by adding them in the Invite Attendees window (see picture), OK, then clicked Send & Close in the New Event window. The attendees received a notification email, since the Notify Attendees box was checked in the initial New Event window. When I deleted the event, a cancellation message was automatically sent to the attendees. This is all done with a calendar added to TB with the built-in CardDAV option. So, I'm not sure what your issue is, except maybe there is no confirmation that invitations have been sent, or no message in the Sent Mail folder.