ProPublica got a tip from a reader named Teressa. Her husband was having a severe mental health crisis, and her health insurance company was denying coverage for his hospital and inpatient treatment. She was fighting back against the denials — and recording every phone call with the company as she did. She brought reporter Duaa Eldeib along for the journey, which ended after Teressa was able to deploy what one source called the industry’s “best-kept secret.”Reporter: Duaa EldeibHow to file an external appeal: https://www.propublica.org/article/health-insurance-denial-external-reviewSupport our journalism by donating at propublica.org/donate.