Notifications

Hi, since a week, every time a get a notification on my iPhone from the app Messenger from Facebook, I get the exact same notification from the Facebook-app itself. I'll give you an example:

Some person sends me a text on the app Messenger. I get the notification from that app, but about one second later, I get the exact same notification from the app Facebook. That second notification then says 'Person A has sent you a message'.

This started about a week a go, on a random day, I never changed any settings of any kind. I already looked on several other support sites from Facebook or Messenger and I can't seem to find an answer. Has anyone ever had the same experience and knows how to fix this double-notification-problem?

Thanks a lot!