Hey Chris,
Sorry to hear about this!
First, I would recommend dealing with this from a security level on your own site. Change the person’s password or something, delete the user account, etc., whatever is necessary to prevent this from continuing to happen.
As for deleting events, is this one long series of recurring events? Or just a bunch of individual events? In either case, searching for a “bulk deletion” plugin on WordPress.org (which are all free) is the best recommendation I can make here—there are many options, so head over, search, and pick one that looks/feels right to you. → https://wordpress.org/plugins/search.php?q=bulk+delete S
I hope that helps!
George