Duy Hoa Tran, a retired Vietnamese schoolteacher, arrived in Los Angeles in February 2020 to visit his daughter and 2-month-old grandson. Two weeks later, the door closed behind him. To prevent the spread of COVID-19, Vietnam shut its borders. No commercial flights would be allowed into the country for the next 18 months.

Tran’s daughter, An Tran, who has a doctorate in business administration and teaches marketing at the University of La Verne, did what she thought was necessary to ensure medical coverage for her then-65-year-old father during the pandemic. But the only option for a visitor on a tourist visa was travel insurance. In early March 2020, An Tran found and purchased a policy, for about $350 a month, from a company called Seven Corners.

She might as well not have bothered.

The elder Tran had been staying at An’s home in Diamond Bar about a year when he told his daughter he was having trouble seeing out of his right eye. A visit to an ophthalmologist produced a solemn verdict: Tran had severe glaucoma and would quickly go blind unless he got surgery.

Seven Corners gave written preapproval for the procedures recommended by Dr. Brian Chen. To be safe, An Tran called the insurer “many times” to confirm it would cover the expense, but no one she spoke with would give her a definitive answer, she said. Chen, however, assured An that insurance companies typically covered the treatment, which was pretty routine.

On April 19, Tran underwent the first of three eye surgeries to resolve the glaucoma. The surgeries — the last was on July 19 — were successful. And then on Aug. 5, Seven Corners sent An Tran a denial of service letter.

An Tran and her father were on the hook for nearly $38,000 in medical bills, although Seven Corners had preauthorized the surgery and she had paid around $6,000 for the insurance over the previous year and a half.