I do get communications from strangers on WhatsApp. Now there is a facility to silence calls like these, although they will still show in the calls tab and notifications.
Press the menu icon, then ‘settings’ and ‘privacy’. Now find ‘calls’ and now one can s’ilence unknown callers’.
It is also possible to block contacts in chats. Go to the chat with whoever you wish to block, press the menu icon, then ‘more’ to get to ‘block’ – and ‘report’ for this contact if you feel it is inappropriate.