Calendar won't delete or stay hidden

Hey out there! I'm having some real problems with my Mac Calendar. One of my calendars marked 'Calendar' has a lot of old events that I just cannot delete no matter what I do. They seem to be deleted but then they re-populate the calendar in a matter of seconds. I can't even delete the calendar, either in my Mac or in my iPhone. Same thing, in that it seems to be deleted but then it pops right back up and won't stay deleted. I've tried hiding the problematic calendar but even that won't stay hidden. Anyone have any ideas about how to fix this problem? If not, are there better third party calendars out there that you might recommend? Thanks for any help you can give me.