there's literally at least a dozen alternatives to whatsapp. i mean its my primary app for messaging, but let's be honest, the notifications have always been terribly unreliable, even going back to wp7.5, and it doesn't do anything that tons of other apps couldn't do.
-> there's fb messenger which is now owned by the same people and does a very very similar thing, there's viber, chaton, snapchat instagram messages and i dont even know what else. get on facebook tell your friend "hey whatsapp is ****ed on my phone, wanna switch to [insert chat name]" [yeah, cool] done.
it's really not at all hard to find an alternative