Scams on calendar

See:

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

If you accepted a suspicious Calendar invitation

If you get an unwanted or suspicious calendar invitation in Mail or Calendar, you can report it as Junk in iCloud.

To delete an invitation that you already accepted, tap the event, then tap Decline or Delete Event. If you unintentionally subscribed to a calendar you didn't want, open the Calendar app, tap Calendars and look for an unknown or suspicious calendar. Tap the calendar, then scroll down and tap Delete Calendar.

Good luck!

Go to Settings>Calendar>Accounts>...and remove the spam calendar.