Unsolicited Calendar invitations
How do I clear virus of my iPhone 7 calendar
[Re-Titled by Moderator]
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.