How to mass-delete outdated repeating invitations in Apple calendar?

In my calendar there are repeating calendar invitations for weekly committee meetings that no longer happen. I have asked the senders to delete them, and they've had a look and said they can't see anything at their end.

At least one-third the invitations are from staff/email addresses that no longer exist.

For each invitation, I click on it and choose "decline", but if I then choose 'save for all events', it gives a brief flicker out then flares back into life, along with all its weekly repeating companions. If I select 'save for this event only', that kills the individual entry but none of the weekly repeats.

There are 45 of these ghost invitations cluttering up my calendar from now until eternity. Every few weeks I spend time individually deleting every one of these invitations for the next few weeks. It's not going to kill me to do it every week for the rest of my life, but my finger gets sore and today I felt like I was losing the will to live. Can anyone help? There must be a hack somewhere!

PS Applies to iPhone, iPad, MacBook, every Apple device in my life. It's the calendar.