This should be a civil case; not a criminal case.  As a civil case, you could be subject to a wage garnishment, lien on your property, etc.  As a civil case, you don't need to worry about jail.  There won't be any jail sentence in a civil case.If the overpayment was due to fraud, then it could be a criminal case as well as a civil case as fraud is both civil and criminal.  A criminal prosecution for fraud could result in a jail sentence.