17 year old debt

[dsuds]

What is the name of your state? Illinois
A collection agency phoned my home and talked to my wife [ I was at work at the time ], about a debt that I owe. He told her the current balance was $12,000 but if I would send check for $6,000 it would take care of it. He said last payment was made in Jan 1990. I nor my ex-wife whom I was married to in 1990 have no memory of this debt. I phoned collection agency next day to find out about this and all he wanted to do was get me to commit to a payment [which i did not do]. They sent me paper on debt but really doesn't say anything, they phoned back a couple days later and I told them I would dispute debt. I have a couple of questions, should I write a letter for disputing debt, should I hire attorney now or wait to see what they do next, can collection agency legally discuss debt with my wife on phone. also collection agency from Florida,1990 I lived in S. Carolina, moved to missouri in Oct 1990 and to Illinois in may 2005 thank you for any help you can give