Exorbitant roaming charge during deployment

Hi. I'm currently deployed to Germany for the military. I purchased a global pass for my mobile plan and have had it active since I arrived in October. 

At the end of October, I needed to travel through parts of Africa and only realized once I arrived that my international coverage didn't extend outside of Europe.

I called Xfinity Mobile international customer service and asked what to do and then proceeded to turn on my roaming and data for the duration of my time in Africa, per their advice. They assured me that I would not be charged because I'd caught it and stopped using the data within a matter of 8 hours or less. 

I've since received multiple automated messages saying I owe upwards of $6,700, that they're going to shut off my mobile service and that it's being reported to a collection agency, which means it's impacting my credit score.

I called and was assured 3 times that the charge would be removed from my account. Then, when I called again tonight, I was told that my case was being forwarded to an "advanced care team" for an investigation that might last weeks (all while still impacting my credit and I'm still receiving text messages saying I'm at risk of losing my service).

I need this to be addressed as soon as possible.