I can't delete a calendar event I did not create I have a calendar event that I did not create but is recurring.  I have declined the request, yet it still shows up on my calendar.  Because I did not create it, I can't delete the event.
My first thought would be to disconnect the calendar (I'm assuming this is a shared calendar of some kind) on all your devices, and then reconnect the calendar to see if the reoccurring deleted event still happens. 

If the event is still getting downloaded to your device and spamming you constantly, you may need to contact the creator of the event to remove it from the calendar or otherwise change some settings.

(Is the calendar causing you problems using Exchange, iCloud CalDAV or Gmail CalDAV? I tend to find Gmail CalDav really finicky with iOS devices especially.)