If your contacts appear in the Whatsapp twice, this is due to the synchronization of your contacts with other services. It may be caused, among other things, iCloud, Outlook, Yahoo, or Hotmail.
Duplicate Whatsapp contacts through synchronization
Through the activation of services such as iCloud, you can have your phonebook now has two groups: the iPhone and iCloud contacts. Whatsapp to see the contacts twice, in both groups, because Apps can not distinguish between the groups. In order for your contacts to appear twice in Whatsapp, please follow these steps:
Open the contacts App and click on the top left on the Button "groups".
You see there are two or more groups, you need to opt for a. You deleted the contacts on your phone and let the iCloud contacts left.
You can either delete each contact individually by Hand, or you can go to icloud.com and delete a whole list.
The contacts in your address book are now only available, they are displayed in Whatsapp only once.
Radical solution: synchronization of contacts to disable
You do not want to stay long with the deletion of the duplicate contacts, you can turn off the contacts syncing with iCloud is simple. You do not do this but only if you need your contacts in the iCloud, and it is sufficient that they are on your iPhone.
Open the "settings"App.
Scroll the menu down and select "iCloud".
Then, uncheck the item "contacts" (see image).
Finally, click on the red print Button delete From my iPhone. You have now only the contacts that are stored on your device. In addition, in the iCloud saved data has been deleted.
Before you follow one of the two steps, you should perform a Backup so that no contact is being accidentally deleted forever.