How many email accounts do you have configured on your device? For instance, if you have iCloud, Gmail, Hotmail, etcetera configured, go into the mail settings and turn off the calendars for each except your Google calendar. Hopefully, that will take care of your issue.
I only have google calendars syncing to my iphone. The issue was created just over time and all the syncing to other places. There are great apps to delete duplicate contacts, I am just not finding that many for calendar entries.