Unfair denial of claim by AARP/United Healthcare

AARP / United Healthcare refused to accept and honor a claim I filed after AARP / United Healthcare Advantage recouped a $407.90 charge 16 MONTHS after they paid the claim submitted by my service provider. This happened during the time I was changing coverage from a United Healthcare Medicare Advantage Plan to a United Healthcare Supplemental Plan. I was never informed that my coverage had changed before the service was provided, continuing to believe at the time that I was still covered under my Medicare Advantage plan. United Healthcare steadfastly held that since the refiled claim and appeal was made more than 12 months later, the claim was denied, regardless of responsibility. I do not know whether Medicare Advantage deliberately or unintentionally waited 16 months to recoup the charge so that any subsequent claim would be denied. Either way the results are the same and I was stuck with the consequences of Medicare Advantage's two failures (1) to validate my coverage in the first instance and, (2) to recoup the charges in a timely manner so that my provider could re-file.