Why is my phone number already in WhatsApp?
All WhatsApp accounts are tied to mobile phone numbers. Since it is common for phone numbers to be recycled by mobile providers, it is possible that the previous owner of your current phone number used WhatsApp.
If the previous owner of your phone number did not delete his / her WhatsApp account, then you and your friends may see your phone number in WhatsApp before you activate a new account. You may also see someone else's profile photo and status message attached to your phone number.
There is no reason to worry in this case. This only means that the previous account was not deleted, so old information still exists in the system. This does not mean that the previous owner of the phone number has any access to the WhatsApp account you activate with your new phone number. Your conversations and other WhatsApp data are secure.
To help eliminate confusion with recycled phone numbers, we monitor account inactivity. If an account is unused for 45 days and then becomes newly activated on a different mobile device, we take this as a sign that a number has been recycled. At this time, we will remove the old account data tied to the phone number - like the profile photo and status.
WhatsApp Support Team