The Justice Department’s years-long court battle to force UnitedHealth Group to return billions of dollars in alleged Medicare Advantage overpayments hit a major setback Monday when a special master ruled the government had failed to prove its case.

The case began with a whistleblower who said UnitedHealth bilked billions of dollars through the Medicare Advantage program.

UnitedHealth Group notched a major court win in a legal challenge over its Medicare Advantage billing practices that is stretching into its second decade. | UnitedHealth Group notched a major court win in a legal challenge over its Medicare Advantage billing practices that is stretching into its second decade.

UnitedHealthcare gained the most Medicare Advantage members during annual enrollment while Humana lost the most policyholders.