My wifes ex has filed bankruptcy, and some of his debt is defaulting to my wife.

We live in Ohio. During my wifes previous marriage, she co-signed a consolidation loan for her then-husband, to pay off credit cards he had charged up previous to the marriage. Then, during the divorce, my wife, her ex, each of their lawyers, and the judge all signed a document stating that that consolidation loan was not dischargeable under bankruptcy, and that my wife was in no way responsible for it. Now, 3 years later, he has filed for bankruptcy, and we have gotten notification from a collection agency that we are responsible for that same debt. The amount is around $1600.00, which isn't huge, but we still refuse to pay one cent of it. We have spoken to his bankruptcy lawyer, who said that we could sue him under comtempt of court, for going against the signed document stating that my wife was not responsible for this. So, I would like some advice on what steps we can and should take to return the responsibility to the rightful owner. Thank you.