* Medicare Advantage: April 2020 CMS and Internal Company Enrollment Data. Medicare Supplement: From a report prepared for UnitedHealthcare Insurance Company by Gongos, Inc., "Substantiation of Advertising Claims Concerning AARP Medicare Supplement Insurance Plans," August 2020, www.uhcmedsupstats.com or call 1-800-272-2146 to request a copy of the full report..