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You've got to figure out from which calendar each occurence is originating straighten that out.

Also, there's a "US Holidays" calendar at the bottom of my iOS calendar list that says "Subscribed" and I assume it's built into iOS. I uncheck it as my holidays are in my Google calendar.
 
go into the calendar app and click "calendars" at the bottom. Uncheck all but one "holidays"
 
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