Basically, you need to go to the Contacts app > Settings > About contacts > click on Contacts 9 times for the 3rd party apps menu to appear and then enable WhatsApp there. You should then be able to text and call contacts via WhatsApp.
Basically, you need to go to the Contacts app > Settings > About contacts > click on Contacts 9 times for the 3rd party apps menu to appear and then enable WhatsApp there. You should then be able to text and call contacts via WhatsApp.