What kind of accountability do employees have? Why can't my card be charged back?

I recently got a call saying to call Cox back. I called a couple days later because my schedule is hectic and I figured it was about my refund they said I was supposed to get. I went to my online account first to see of they had a message of some sort and they said I owe $35. I called and they said I owe them for modem I didn't turn back in. Luckily I still have the modem and that I'm in the States... for now. The thing is that I was told I owned the modem when I got the service canceled. I have a local solution shop so I can turn it in but this is going to end VERY bad for another Sailor/Marine where they provide internet. I wasn't SUPPOSED to be in the States right now. I have orders to Japan but I was able to go to a school beforehand. I just happened to be in a place where I actually have Cox near me while still in possession of the modem before I canceled my phone service before leaving the United States. I need to maintain a clearance and collections is an easy way to lose it. No clearance, means I have no job anymore. This would have been because of a negligent  employee.  Someone would have lost their livelihood because an employee didn't care to check or was ill-informed on procedure.

My second question is simple but lead to more questions. Why can't my card be charged back if that's what I paid my bills with? Since you clearly provide internet to people that are generally junior Enlisted, why would you mail a check to them? If someone is transferring, how do they think they'll be able to receive this check before actually getting to the location to secure the mail? What sense does it make to tell you to send me mail to location in Japan, of which I don't exactly know yet? Mail has to be addressed very specifically or else it's gone. Why does it take 4-6 weeks when it instantly comes out my account?