Imagine that A owes 5000 dollars on a debt and doesn't pay when it was due. The creditor tries for months to collect from A with no luck, so they send the matter to a collection company. The collection company will receive half of everything they can collect from A. The collection company's employee informs A in writing if he pays $3000, the other $2000 will be written off. A pays the $3000, but the collection company continues to try to get the $2000 from A.

So does A owe the $2000? I think it's not but I'm not sure if it's because stature of frauds or because he made a legally enforcement contract with the collection company.