calendar infected with malware

If running iOS 13 or earlier versions, check: Settings - Passwords & Accounts - Accounts - Any rogue entries here? If so, delete the rogue account. 

If running iOS 14, check: Settings - Calendar - Accounts - Any rogue entries here? If so, delete the rogue account. 

The Apple support article is below. 

Remove calendar spam

Video support

It's highly unlikely that a calendar app on an iPhone would be infected with malware.

I got the same notifications but only have my gmail and iCloud calendars listed in my accounts. Any idea where to go from here?