How do I stop calendar events from being automatically added from mail (I'm getting SPAM)

I have, with some regularity, been getting SPAM calendar invitations in my email. They are being automatically added to my calendar. Of course I don't want to respond, even to decline. I simply delete the event but then I get administrative emails saying that my "response" email could not be delivered (so simply deleting the event appears to be triggering a response to the sender).

I have searched the forums and have turned off the "learn from the app" feature on my iPhone - for both mail and calendars, but I have also seen people posting that this does not solve the problem. Beyond that, I did not seem to find anyone with a solid answer on how to stop the automatic addition of calendar events from email. Help would be appreciated.

Thanks!