In my opinion you are definitely required to respond. The borrower's right to Fair Credit Reporting by the small bank didn't die when it merged. Typically any bank merger agreement specifically details that the surviving institution will assume all debts, obligations and duties of the merging entity. I would contact my Credit Bureau rep to determine how you would go about responding to the dispute given the subscriber number issue.
_________________________
My words and opinions are my own and don't represent my company in any way.