The laws governing the ability of insurance companies to recoup refunds from providers vary by state. A useful Web site that will assist you in finding the law specific for your state is www.AskLeslie.net. For example, this site includes the law for the State of Indiana, which reads as follows:
Claim payment errors
Sec. 10. (a) An insurer may not, more than two (2) years after the date on which an overpayment on a provider claim was made to the provider by the insurer:
(1) request that the provider repay the over-payment; or
(2) adjust a subsequent claim filed by the provider as a method of obtaining reimbursement of the overpayment from the provider.
(b) ...