Hey @Pratt07, 11GB of data is really a lot more than what I have heard from others. But you are not alone. I experienced a similar problem too when the new version of Facebook Messenger was released back in January. Soon after that, I uninstalled official Facebook apps including Messenger and started using Disa (more about alternatives in the end).
Anyways, as far as your problem is concerned, I can clearly see the link there:
So, excessive data consumption was started right after you updated Facebook Messenger to the latest version in April. Seems like the Messenger app even has the permission to override the instruction given by Android about not allowing background data usage. Also, after looking at the list of permissions their app requests, I believe that the people over at Facebook are using mobile apps to steal user data and then sell it to the advertisers. Unfortunately, there's not much we can do about that.
The simplest and the easiest solution is to use third-party apps like:
Else, if you can't trust any of them and want to use the official app then, as recommended by @steve, Facebook Messenger Lite is the only possible option.
Also, please note that all the alternatives I have mentioned above are lightweight, free from bloatware, consumes less data, and does not require an excessive amount of permissions. Though, you might not be able to find all the features of Messenger app.
P.S. Don't forget to setup a monthly data usage limitation to 2GB (or whatever your average data monthly usage is) on your Android phone, which will automatically force-stop the data connection from any further data consumption whenever the limit is reached.