getting crazy notifications from calendar on iphone

I’d tap the calendar button at the bottom, highlighted in green below. (The button at the arrow shows a list of entries, but not an easy path to the calendars.) From the list of calendars, find the spammer’s subscribed calendar. The color of the subscribed calendar entry in the Calendar app listing of calendars should match the color of the spammer’s events. Tap the information ℹ️ button for the subscribed calendar you want to delete, scroll down, and tap the delete button.

Tap this symbol and remove any unfamiliar calendars.

Read and follow the article linked above.