Whatsapp Push notifications not working

Dear all,

I have an iPhone 4S with iOS 8.3. Whatsapp push notifications are not working. I do not get any push notification. I have to open chats to see the activity. When I close the window and I remove it from the multitask push does not work anymore. If I do not remove from the multitask I still get pushes for 2-3 minutes, until iOS closes the app automatically.

I tried all you can imagine:

1. Uninstall / Reinstall Whatsapp app
2. Reset the phone
3. Erase all content
4. Restore from a backup
5. Logout and login from app / itunes store.

Nothing worked as expected and I still do not receive any push notification.

I had the same trouble with Facebook Messenger and Skype. Fortunately, I managed them logging out and logging in again. Nevertheless, Whatsapp has not a logout button. So, I cannot try the same approach.

The only thing that works is to restore the phone as a new. But this means I am going to loose all my messages, photos, chats, progresses on my games or other app data. And since the ifunbox access has been closed, it is impossible to backup app data individually.

Anybody had the same problem and is being able to repair it?

I will appreciate all of your answers. Thank you for your time.