Error Code 2 - Facebook Apps

Past 24 hours, I've been unable to log-in to Facebook and Messenger on both the iPhone X and iPad Pro... continually get 'Sorry, an unexpected error occurred. Please try again later. Error code: 2"... Tried everything to include deleting the apps and reloading them, deleting cookie history (safari), rebooting phone/ipad, resetting network settings, rebooting router... I've contacted both Apple and my WI-FI provider - they believe the Facebook app is at fault (which is great I guess that it's not my devices that are faulty, but it doesn't help me and I can't find any record of anyone else having a similar problem in the past few years).

I have noticed via my phone (my iPad is WIFI only), that if I turn the WI-FI OFF - I can access the apps via 4G (and thus, Facebook clearly has some kind of issue connecting to their servers using my WIFI)... has anyone experienced similar issues and found a solution? I've tried numerous times to just delete and reload the app (which normally works for Facebook glitches) but not this time - It seems to be remembering me, and I'm wondering if there isn't a 'proper' way to delete an app from an iPhone X/iPad Pro? (i.e. as though you are setting up a Facebook account for the first ever time and it wants your log in and password details... as opposed to when I delete the app using either of the two traditional Apple methods, and the Facebook App immediately tries to recognise me and log in automatically via my profile pic)... having changed the password as an additional attempt to resolve the issues, I don't trust that it is attempting to enter the latest information?

My WI-FI is working perfectly from the laptop and for everything on the iPhone and iPad except the Facebook (and Messenger) Apps... I regularly use Messenger for my business (and hence why I am frustrated - the messenger app won't work whilst the Facebook app isn't working)... is there an individual Facebook cache that can be cleared within settings? I've searched everywhere for a method to persuade Apple to 'truly' delete an app without remembering past data, but I can't find anything 😩

Appreciate any help and sorry if I sound stroppy... just tired and fed up now lol... I woke up to this problem 17 hours ago and have done nothing else since but try to resolve it to no avail but a factory reset really isn't an option for me! Very grateful to any help and advice anyone can give.