How do I figure out who to send a QWR to?

[Sandy Uhlmann]

I purchased a note that had a UPB that was near $100,000 on the tape. When all said and done and boarded with a servicer the UPB was recorded as about 3/4 of that number. The borrower admittted to owing the higher number. There was not a payment record that accompanied this note that had been delinquent for approx 5 years. I can follow the chain and assignments to see who owned the note but this does not tell me who the servicer was for the note owner. I believe a qualified written request has to go to the servicer? I want to try to find payment records to prove or disprove the UPB. Any suggestions would be appreciated.