Be that as it may, the law in California forbids the insurance company from refusing to pay at the in-network rate in an emergency. As evidence, I'd submit the claim they immediately paid when called out on this.

If the insurance company weren't cynically exploiting people's lack of knowing their rights, they'd at least send a form letter to the patient saying "Please send us whatever proof from the hospital that you had a legitimate emergency and if approved, we'll pay <insert details> percent." Instead, they pay nothing, shove their fingers in their ears, and let the balance bill come to the patient, and hope nobody tells on them.

The only ambulance rides that should be billed like this are frivolous ones, like if someone is rear-ended at 1MPH, are unharmed, and they lay on the ground and fake an injury and demand to be transported to try to support a fraudulent legal case.

But isn't the California law requiring the insurance company to act as a sin-eater here? They seem to be the only people you were frustrated with, even though they are not the ones who charged you $1000.