I actually did, and here is the answer I received:
"When you are sent a message in WhatsApp, but are not online to receive it, WhatsApp will automatically send your message to the Apple Push Notification Service (APNS). This allows an alert containing the message to be displayed, even when WhatsApp is closed or your phone's display is off. Most often, all that is needed to resolve notification issues is to ensure that all notification settings are enabled. Review these FAQ pages for troubleshooting steps:
Sending your message to APNS typically takes only a few milliseconds. Once your message is sent to APNS, any delays or failure to deliver the message as a push notification to your device are usually caused by issues with your phone or network connection. Currently, all of our systems are operating normally.
If you are using iOS 7, and are confident that you have all push notification settings enabled in WhatsApp and the iPhone Notification Center, then there is likely an issue with your phone that WhatsApp cannot resolve for you. In this case, I recommend the following steps:
- Backup your entire phone to iCloud.
- After the backup is complete, Erase all content and settings.
- Continue setting up your phone as a new device (do not restore from the iCloud backup).
- Install WhatsApp and verify that push notifications are working correctly (have someone send you a few test messages while your phone's display is turned off).
- Erase all content and settings and restore from the iCloud backup. "
I tried to delete everything from my iPhone and then restore my data with the backup on my computer but it did not change anything, I still can't receive any notification, unless I open the application... However, I restored immediatly my backup cause I was afraid it wouldn't work after, but I don't really think it would change something to first start as a new device and then erase all content again and restore it.