Paid twice to Arrow Financial

I paid Wells Fargo the money they said they were owed, but in a letter from them they stated the money was sent to Aarow as they were the assingee of Wells Fargo, BUT Aarow Financial was also sent a check in the amount of $4454 for the same account as Wells fargo was paid for, A certified letter to Jack levin, president, has not been answered, letter requests payment of the overage of $3950 to Wells fargo, I would dedfinitely question their, HONESTY, INTERGITY, ETHICS, MORALS. WHAT can I do to convince that firm to be HONEST? I beleive there is an Illinois statute about excess enrichment, how do I go about useing that statute?
Bob