I have the exact same story as YeaMe. My insurance wouldn't cover bariatric surgery, so I paid out of pocket. Afterwards, I asked the hospital to bill the insurance for some blood work, which I considered standard health care. Apparently, they sent the whole bill to the insurance, and the insurance paid 2/3 of the bill! They did not approve the surgeon and anesthesiologist charges, but everything else. So the hospital is sending me a refund for the difference ($11,000+). Needless to say, I'm very pleased and surprised.