Whether you have legal recourse is a complicated question. It mostly turns on whether the underlying debt is still good.
You could challenge the debt as being uncollectable because it has passed the statute of limitations
. The statute of limitations on a debt depends on what state you are in. It starts running from the date of your last payment on the debt. If it is past the statute of limitations, then you have a defense.
Also, the debt collector has to have the underlying paperwork that supports the debt, such as the original agreement that you made to pay the debt. If we are talking about a credit card, this means the original paperwork (sometimes without a signature depending on how you applied for the credit). If they don't have the paperwork, you can deny that you owe the debt.
Finally, depending on your state, you may be judgment proof. That is, all of your assets may be beyond the reach of being seized by a judgment. In that case, you could tell the debt collector that you have no money to satisfy a judgment anyway. If they go get a judgment, you could simply represent your self, and deny that you owe the money asserted, that they calculated the interest wrong, that you never agreed to the interest rate, etc. If they get a judgment, then you can tell them they can't really do anything with it if you are judgment proof.
You can always try to call them and enter into a payment plan too. Sometimes they play hard and try to insist that you pay the entire settlement amount, but if you ignore them long enough, they will often accept a much lower amount than what they are asking now, and may agree to a payment plan.
I hope this answers your questions.
Zachary D. Norris