I'm currently arguing with my health insurance about their refusal to cover a treatment because they allegedly haven't received the required documentation. This

I'm currently arguing with my health insurance about their refusal to cover a treatment because they allegedly haven't received the required documentation. This is after faxing these documents to a number that turned out to be a black hole, attaching a PDF to a message in their messaging portal, and eventually sending it by certified letter, complete with a returned delivery confirmation. Today I got a letter in the mail saying that my grievance was denied because they've yet to receive the necessary documents to process my claim. Here I am paying out of pocket for a medically necessary and covered service simply because the insurance company is playing games. I would prefer they not try to cut their costs by playing stupid games like this about valid claims in the hope that I just give up so they don't have to pay. It's feeling like I'm going to have to sue them to get this resolved. At least it's harder for corporations to play games with process service.