Push Notifications are not working on my iphone 4
I had a locked AT&T iphone which I recently unlocked paying for it through Negri Electronics (Apple approved), this means that I can update my iphone through iTunes without any problems, which I did and now I'm using another carrier chip.
I see that my notifications are enabled but they are not working at all. For example my Whatsapp is not receiving any messages unless I open it up. This happens with alot of other apps that use notifications.
FYI. My iPhone 4 is not jailbroken and has the latest update.
iPhone 4, iOS 5.1.1