My Calendar has been hacked
How to delete link I my 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.
https://support.apple.com/en-us/HT211076