Unwanted calendar events

Hello! Make sure you remove spam or unwanted invitations and notification in your Calendar. You may follow the steps on this website for more information: Remove spam from Calendar on your iPhone

If running iOS 13, 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.