Why is my insurance rejecting a surgery claim they already paid for?

My wife was suffering with severe acid reflux for over two years. It affected her quality of life, her job, and her ability to speak for a long time. It hurt to see her suffering so much. Every morning & night she couldn't sleep, eat, or talk because the pain was so bad. So, after meeting with several dr's they confirmed the root cause of the problem. She had a severe hiatal hernia that created a large gap in her esophagus.
She had the surgery in January and we paid the bill in February, it was well over 100k for the surgery. Insurance paid like 99% of it, we paid 3.5k. My wife's been back to her normal self, eating food she enjoys, back to her standard quality of life, and she's not experiencing any more pain!
We got a letter in the mail saying they rejected our claim because "there is no proof or not enough proof that it improves health". It was reviewed by a pediatric dr which boggles my mind that that's allowed.. What do I even do? We already paid our portion of the bill!
I'm at a loss, I'm anxious, worried because we've been trying to get a house this year and this may screw it up.. I don't know what to do and where to go from here. How can they reject a claim 4 months after the fact and after they already paid it?

Any help is greatly appreciated!

submitted by /u/ethiofreak
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