Why spam notifications are automatically added to Calendar on my iPhone

Spam solicitations are now being automatically added to my calendar on my iPhone. Each day I’m getting now 10-20 unsolicited ads entered on my calendar as ‘events’ even though they’re just unwanted ads or links to ads. It’s starting to make my calendar useless as I can’t even see my actual calendar appointments without scrolling down far. How do I stop ‘events’ being automatically added to my calendar?

[Re-Titled by Moderator]