Is there is a time limit for insurance companies to request refunds from providers? 

Refunds are a contractual issue. Look at your payer contract for limits on "recoupment." If there is no time limit, they can seek refunds for as far back as they like. Many physicians try to address this issue when it comes time to make or renew contracts.

Also, some states impose limits. For example, according to the Texas Medical Association, "state-regulated insurers and HMOs (which account for 20 percent of the market) [in Texas] may recoup overpayments only for those claims paid 180 days prior to the refund request."

Is there is a time limit for insurance companies to request refunds from providers?