I am not licensed in your state but I can offer some general advice.
I have not seen the form so I am no sure what it says, but I will take a guess. I would suspect that since the debt is 10 years old it is outside the statute of limitation so legally there is nothing that your creditor can do to compel you to pay. Except, if you reaffirm that you owe the debt then they can. I suspect this is what the form was all about. I think it is good that you did not sign it. I would not have. In fact I would not even bother with them.
As for the IRS issue. The tax code says that any time you get any sort ascension to wealth it is a taxable benefit. So if you have a debt forgiven you have improved your financial position and that is a taxable benefit. However, in your case you may be able to argue with the IRS that you were no longer legally liable for the debt thus there really was not ascension to wealth in your case.
I think you can just ignore them, but you really should get advice from a local lawyer who will know what to do before taking any course of action.
You should talk to a local lawyer who will be able to give you advice regarding your situation and your jurisdictions laws.