We have had a number of things that had to go to a "peer to peer." I also tend to call insurance after a while, and I also often get the claim that the doctor's office hasn't sent what I know has been sent. That's clearly one of their ploys, but the good news is that so far, we've always gotten approval in the end. The docs seem to know what they need to say to get approval, and I don't know whether my calling has generally made any difference, but what I do know is that I once managed to get the number of a supervisor who was actually very reasonable, and every time that my kids move to a different state (which happens quite often since they are in college out of state, gets summer jobs, etc), she streamlines the approval process in the new state so that they aren't late for their meds, so it has been worth my calling for that.
BTW, I resent the term "peer to peer" because they are not peers - it's our specialist in IBD who knows my kid talking with someone with a general MD that the insurance company has hired to cut costs.