Ok, so the mortgage company repo'd the house and tore it down because the land value alone was greater than the house. So the mortgage company is going after them for the remainder of the home equity loan after the land was sold and the money applied to the expenses of the repo and towards the loan..
Mortgage companies aren't in the business of bulldozing houses.
Last month. His ex is actively paying her half.
Has he ever made any effort to pay off the loan?
No. He claims he didn't remember signing the document.
He can stop that. He has the right under the federal Fair Debt Collection Practices Act (FDCPA) to tell the collector to stop contacting him about the debt. He needs do that in writing. The federal Consumer Finance Protection Board has a sample letter in Microsoft word format that he can use for that purpose. Note that this only works for third party debt collectors; the FDCPA does not apply the original creditor (mortgage company) itself. Once the collector gets that letter it must stop all contacts with him about the debt except to inform him of actions it WILL take (not that it might take) to collect, e.g. suing him for judgment. The collector might dump this debt off to some other collection agency, in which case he'd need to send a letter to the new collection agency.
This all makes very little sense, and you didn't answer a lot of the questions I asked. For example, I still can't tell what the mortgage has to do with the home remodeling contract you initially asked about, and it sounds like a lot of the relevant events took place so long ago that relevant statutes of limitations may have expired.
How recently? I assume she has missed payments or not made payments in the amounts required, hence the collection letters.
How actively? Has she only paid “half” of the payments due? Did she expect or assume her ex, the blind man, was paying the other half? Was the man ordered as part of a divorce agreement to continue paying half of what was owed?