Do you have that in writing? :confused:

In my case a divorce decree was granted by the court that took judicial notice of the property settlement agreement (which also incorporated child custody and support terms). The settlement is itself a contract between the divorcing parties. .
A divorce property settlement can be either a contract between the divorcing parties, or it can be the order of a court; it's binding on the divorcing parties in either case.

That said, if party A has a debt to party B, a promise by party C made to B to settle the debt on A's behalf, (be it in a contract or in compliance with a court order) does not discharge A's responsibility to B, and the debt does not magically become "C's debt"...even if C was a debtor to A as well. In that last case the credit contract language is usually that the debtors are "severally" (individually) liable for satisfaction of the debt as well as "jointly" (together)--they're both on the hook for the full amount. If the resulting lawsuit is a surprise, it's only because A didn't verify C's performance and enforce the contract containing the promise. But that's a matter between B and C; it's not A's problem, nor should it be.

(of course the usual IANAL disclaimer applies. )

Curious as to why the divorce settlement issue was not mentioned in the OP and indeed until now, as this clearly affects any advice on how to proceed, which was the question in the OP :?