Substitution Of Counsel filing

Location: NC

My wife received a letter from an atty's office which began:

"Our firm has been retained by [CA] to replace their former attorneys in this case. Because we are replacing the prior attorneys for the plantiff, we are required to give you the following notices: Please again take notice that judgement was entered against you in the above referenced case on or about May 15, 2006. The current outstanding balance of the debt is [$x]. You should be aware, however, that interest is continuing to accrue on the account."

The letter went on to explain, "If you dispute this debt,..." ... 30 days to send VD, etc. and another paragraph, "If you have already made satisfactory arrangements to pay this debt, please make all future payable to [CA] and send them directly to our office [Atty's]..."

It was sent with a copy of a letter and Notice of Sub of Counsel mailed to the Clerk of Court here.

I did go to the clerk of courts & there was indeed a judgement made. The summons was served on a vacant house (according to the deputy), a former residence of my wife. She had no knowledge that this suit was even taking place.

Further, the debt was paid in full, but she has no records of payment or statements, etc. since it was back in '05, '06. Additionally, the debt does not appear on her credit reports.

Questions:

1. Since it seems to be a notice of sub. of counsel, is this something we really need to respond to? What should her response be? She doesn't acknowledge the debt as it was paid. (the last line of the letter does state that it is an attempt to collect a debt.)
2. I believe the SOL has expired, though as I said, the debt was paid.

Any thoughts. Thank you.