Settlement with First USA

First USA says we owe them about $5000 from a credit card that was opened in 1999. They've never contacted us....they've always used a collection agency (NCO). Our attorney is in the process of closing the account with NCO and recommended that we go to First USA and talk to them about any underlying balance (even though NCO told us we paid off, they now have been telling us we didn't).

Should I contact First USA? Even though they have never contacted us?

Has anyone ever successfully negotiated with First USA?

What would be recommended settlement amount for a supposed debt of $5000?

Any input is appreciated. Thanks.