Taking back refunds

I live in WVA. Last June the IRS sent me a $1300.00 tax refund. They sent no letter of explanation. Now they just sent me a letter stating that I have to give it back beacuse it was an error. (They are so considerate and are letting me have until Feb 2nd to pay it without having to pay interest). My question is do I really have to pay it back? Is there any law that protects a Citizen believing in good faith that the IRS knows what the heck they are doing and accepts a refund?

Thanks

MY QUESTION IS DO I REALLY HAVE TO PAY IT BACK?
Yes, you have to pay it back.

IS THERE ANY LAW THAT PROTECTS A CITIZEN BELIEVING IN GOOD FAITH THAT THE IRS KNOWS WHAT THE HECK THEY ARE DOING AND ACCEPTS A REFUND?
No, there is no such law. If you were entitled to the refund under the tax law, you could keep it. But if they send you money be mistake, you must pay it back. The same is true in reverse: if you send in money by mistake, they must return it.