What can I do if I got a letter in the mail from a former attorney I used 3 1/2 years ago saying he is going to sue me for unpaid debt?

Do you owe money to the attorney? Its going to sound snarky, but think about this with some common sense. If you owed money to the attorney for legal work and did not pay, what did you think was going to happen here? If you owe the money, then the option is to pay it or work out some kind of agreement. If the lawyer sues and you do nothing, the lawyer will get a judgment against you and be able to garnish your wages and seize any assets owned free and clear. If you have any valid defenses to the charges (example, the attorney over-billed or did not credit some payments) then you should get a lawyer and file an answer to the complaint. You only have 30 days to answer. If you have a lot of debts and just cannot pay, then you may want to consider bankruptcy. If you work out any agreement, then you should get it in writing. The lawyer may send you a consent order or agreement if a lawsuit has been filed. Get clarification on whether any interest will be charged and if you make a payment plan stick to it. Keep track of all your payments.