The 3rd party vendor who handles my company's payroll notified me after my W-2 was issued and they didn't show me any documentation of how they calculated the amount of overpayment. I asked for a copy of the policy and procedure of what happens in an overpayment situation and for an explanation of the overpayment calculations. They said they would do another audit. They then came back stating the findings were the same, but still provided no proof. When I asked again for an explanation and policy and procedure, they changed the amount. I am still not confident the amount is correct but because so much time has passed they are now demanding a lump sum payment and threatening bad performance reviews if I fail to pay by 12/27/13. What are my rights? Do they have to provide me a policy?