Help setting up Mobile Broadband

Ok, I’m gonna be real with everyone, I have a very unusual setup which is probably responsible for my problem.
I’m a student and I need to bring a Chromebook/laptop to school. I don’t particularly trust the school Chromebooks since they have a lot of monitoring software, so I decided to re-use my old Pixel Chromebook from 2013 instead. (Even though it is quite old it still does hold up today especially compared to other Chromebooks) I went ahead and installed Manjaro on it, flashed the bios with a UEFI bios, etc, and it works just fine.
However, the only thing that doesn’t work is the LTE card, and I can’t figure out why.
I’d much prefer to use cellular directly rather than relying on using my phone as a hotspot since it means I don’t use as much battery and can get faster internet speeds.
I have a spare sim card I can use and it works just fine in my phone, however it doesn’t appear to work in the Chromebook. Trying to connect to cellular network works for a split second before I get kicked off the network. I’m not super well versed in Linux (especially technical problems), can anyone help me out?

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