( December 9, 2024, 9:20 AM EST) -- CHICAGO — Alleging that they were paid only about 8% of what they billed for out-of-network services because of “a buyers’ cartel dating back to at least 2015,” medical practices that refer to themselves as doctors sued MultiPlan Corp., Aetna Inc., The Cigna Group, UnitedHealth Group Inc., Elevance Health Inc. and other entities in Illinois federal court, asserting numerous claims including some under the Employee Retirement Income Security Act....