Not everybody in the call center of your health insurance policy is an insensitive prick. Sure, a lot are, but be patient and you may be able to get your denied claim overturned. A lot of this may seem like common sense, but just in case it helps someone...
Always, always be polite to the phone rep. Same goes for the staff at the doctor's office, no matter how shitty their folks in the billing department are. They may not be helpful at first, but they'll shut down immediately if you're rude.
Locate your policy and read it thoroughly. Use
Webmd.com and similar medical websites to research your condition so you know your shit. Nothing makes a lazy or jaded phone rep sit up in their chair like a caller who can politely point them to "Section B, item 37 on page 19 where it specifically mentions that "X" is covered if conditions blah-blah-blah are met, so why was my claim denied?" At this point they'll either decide they need to help you, or send you to a supervisor, either of which improves your chances.
Figure out the *real* reason your claim got denied and have your doctor's office provide notes supporting why the denied treatment was appropriate for your condition. Did the insurance company feel it was not medically necessary? Was the treatment considered experimental? Did you have to use a non-network provider because your network didn't have someone available? Did they say you didn't have prior authorization, when you know a call was made? (You wrote down the date, time, and rep's name when you called, right?) One you get to the root of the issue, you can address your written complaints more specifically and improve your chances.
KEEP INSANELY DETAILED NOTES. If you press them, you can almost always get the name and extension for the rep you spoke with, and a reference number for the call. The date and reference number are helpful in cases where a call center allows reps to use fake names on the phone. My company used real names, but not all do. Make note of date/time, etc. **This is especially important when you get someone who really goes out of their way to help you.**
Politely ask for the last person you spoke with, or the person who helped you the most last time when you have to call back. It won't always work, but if there's a ton of case notes from the last call, the new rep will likely see them and not want to get in the middle of it. This helps you and the rep.
It's easy to get frustrated and want to yell at the rep on the phone; but when I was taking calls I actually enjoyed helping someone in genuine need of assistance. I HATED seeing legitimate claims get ignored. It felt good to have someone say "I've talked to 5 people here, and you're the first one to really help me". So the being polite part cannot be over-emphasized.
Read up on your insurance company's appeal procedures, and use them. Many people get exhausted by the bureaucracy and let it go. Be persistent. It's not uncommon for an issue to take 18 months to resolve. Keep a notebook of the case history and put reminders on your calendar to call back a week after you were told the next step of the process would be complete.
**NOTE** Please do not do this to try and get reimbursed for a $25 flu shot your plan doesn't cover. Save this stuff for something that really matters.