Do you have a iPhone? Because this description works with iPhone(though you might be able to modify to work on your computer);
go to the calendar app,
click on the event that is annoying,
click on delete event,
then click delete all future events.
that deletes all the events related to it.
If it’s the notifications that are annoying then turn them off on your devices at Settings>notifications>calendar.
If this helps at that page you can also set up custom notifications, which filter out your notifications.
also, check that it’s not a subscription calendar, but if it is then you can go to calendar>calendar and there you can unsubscribe from it.