Medical billing is a nightmare. I have HMO insurance (which means the process should be really streamlined - everything is in-house) and I once tried to figure out why certain rather simple bill item was billed certain cost. It took about three weeks, multiple calls and emails, and speaking to several people, to get to the stage where they said "this is probably because if it was classified as code X, though we can not give you rules why it is code X and not code Y, and there's no way to know upfront which it would be, we'll just send you the bill later and you pay whatever we say" and even then they couldn't answer why sometimes they billed certain percentage upfront and sometimes another, so that you end up getting different pre-payments and different bills for the same thing. This whole thing is an ungodly mess.