Facebook Messenger for iPhone? - 1

I've been using the Facebook Messenger app on my iPhone as my primary app for messages for months now and never had a problem with it. A few days ago though, I noticed that I'm no longer receiving any sort of notification for messages; no banner notification, no '#' in a red bubble (badges i don't know) on the app, nothing - there's no form of notification any more and I don't know when or why this happened.
I've checked all my possible settings in app and out repeatedly, all notifications are on (unless I've missed some?). I've deactivated & reactivated my Facebook account to see if my own account was the issue, nope. I've reinstalled the app many times, still doesn't work. I've plugged my phone into my computer and reinstalled the app there etc., still 0 notifications. I'm all out of ideas and Google isn't cutting it, does anyone know how to fix this?

Don't think it matters, but I have the Facebook app itself on my phone, and never use it (ever). Just deleted it, made no difference to the problem. Where are my notifications! How do I get them back? Help

Added (1). Woops wrong category i cry

Well its the same case for me too. All of a sudden there's no notification at all. Now i can only receive new messages in this app. If iim using other app or just leave my phone in the main screen, no notification appear automatically when people send messages to me