I've worked in insurance 10+ years and can tell you from my experience, we don't sit on paperwork. We have print outs and spreadsheets tracking everything we do. Any correspondence is time stamped and every company has turn-around-time goals. If something gets "old" we're going to be asked what the hold up is. When it comes to pre-approvals, on our end the hold up is with OUR medical staff.
Why is that? IDK. Doctors run on their own time, I think.
And as far as your doctors office not getting back to you, I'd ask if there's an office manager and speak to that person. If they can't help, then tell your surgeon that their staff is irresponsible with returning phone calls. That's not a responsible way to run a practice, and the MD should be aware if an office manager is unable to resolve the issue. I would normally err on the side of patience as well, but when you're lied to (i.e. them saying they didn't get the letter/it's still in nurse review) that's the end of being patient! Did you offer to fax a copy of yours to them? It should have most of the same info...
In any case, try to keep your cool, but don't lay off hounding them to get their jobs done.
good luck!