iPhone 5s no longer receiving notifications

I've had my iPhone 5s for about 6 months now, with no problems. But yesterday it stopped receiving notifications, specifically from Instagram and Twitter. I still receive text messages, and phone calls. Before anyone asks, I have checked the Notifications Settings and everything is how it should be, I've logged in and out, turned the iPhone off and on, and I even erased my entire device and reset it. Still, nothing works and I am not getting notifications. All of the software updates are up to date, and I can't find any reason for this to be happening! What can I do to fix it??