Health insurance company I worked for would automatically reject claims over a certain amount without reviewing them. Just to be dicks and make people have to resubmit. This was over 25 years ago, but it's my understanding many health insurers still pull this shit. They don't care if it's legal or not. Enforcement is lazy and fines are cheaper than medical claims.
We need a whole branch of government dedicated to fucking with insurance companies. They basically generate free money by having money, they don't actually provide any net positive outside of just having money
Definitely sounds like Cigna. Several doctor practices have told me that Cigna rejects alot of insurance claims when other agencies don't give them as many difficulties.