TIA.
WhatsApp in its recent update has changed how the UI looks , there is no more Contacts Tab as there was in the past, as you can see in the image below the Contacts Tab as we all remember is no more
I have covered a blog post tutorial showing how to unlock hidden WhatsApp Features , the same tutorial can be used to enable the old contact tab as shown above, you can achieve that by following :
WhatsApp has removed the Contacts Tab and to see your WhatsApp Contact List
On some Android Mobiles which have a lesser screen dpi are not yet updated to Nougat the Send New Message and see All Contacts button might appear next to the WhatsApp Chat search as shown below
Hope this Helps