I’ve just had a load of notifications come on my iPhone in a calendar

it looks like you have subscribed to a spam calendar that ads this kind of crap to your calendar. to delete it go to settings-calendar-accounts-calendar subscriptions, find the disturbing one and delete it. done. hope this helps

This might prove to be helpful.

Delete spam calendars and events on iPhone - Apple Support

You are right about not clicking on them. Try erasing or deleting the calendar.