iPhone Users when upgraded to iOS 10 are facing a issue with iCal that birthday entries have duplicated multiple times, calendar app has duplicated the birthdays calendar hundreds of times - both on the Facebook calendar group and my default home calendar group. It has also duplicated my default calendar hundreds of times. it's not only the Facebook calendars. It's also duplicating the Birthday calendars under the calendar group named 'Other'. This suggests it's an Apple problem too. Some users have around 180 instances of "Birthday" calendars under a group called "Other". checked my iMac and these birthday calendar instances (duplicates) do not appear there. It is only on my iPhone.
Fix 1: Update the Apple iOS version
This is been sure fix to remove duplicate birthday enrtry from iOS device or iphone. Update to release of iOS 10.3 and it has fixed the issue for so many users.
Fix 2: Following steps may help you to resolve the issue.
Deleted all accounts (comprising of iCloud & Gmail) from Settings>Calendars>Accounts
Disabled Contacts and Calendars from iCloud.
Disabled “Events Found in Apps” in Settings>Calendar
Logged out of Facebook in Settings>Facebook.
Deleted Facebook app.
Deleted Calendar app.
Installed iOS 10.3 BETA
Installed Calendar app.
Enabled Contacts and iCloud calendars
Fix 3: Delete Calendar Entry
I was able to finally get rid of the duplicate Birthday calendars the following way.
1. Turn off all calendars on your iOS device in Settings > Mail, Contacts, Calendars
2. Create a complete backup of your iOS device on your computer with iTunes.
3. Make a copy of the backup folder
4. Download and install iBackupbot on your computer
5. Delete the Calendar folder and all Calendar items out of the backup as shown in the screenshots.
Workaround to fix delete birthday calendar iphone
duplicate birthdays in icloud calendar
Delete and disconnect any calendar on your iPhone and that will at least get the phone working normally again. This does not solve the duplicate problem in any way.