Legal Question in Credit and Debt Law in North Carolina

Yes, if you were not legally owed the money, then they can demand a refund.

The question is who made the mistake? When the check arrived, did you think you were entitled to the money? If so, why? If both parties were mistaken, then you would have to refund the money. Same is true if you knew of the company's mistake and did nothing.

If only the company was mistaken and you were innocent, maybe not, but how much is owed? Did you take and use the money? Do you want to end up being sued and spend money on a lawyer to prove that it was just a mistake by the company?

It would be cheaper for you in the long run to just repay the money. If it truly was the company's fault and you acted in good faith, I am sure that you will be able to extract favorable repayment terms. Just get the terms in writing.