Oh man, this is easy. They denied his request because there was no confirmation that they did or did not have information.

send a "Hi how are you" letter to the NSA chief, naming him as a party, with an affidavit stating that the NSA does, in fact, have information on you. Give him 10 days to rebut it. Then give him a second letter, acknowledging his fault/acquiescence to the affidavit. then 10 days after that, send a third notice cementing his agreement to the affidavit's truth.

THEN you go do a FOIA request. Include your paperwork with the FOIA request. They can't refuse, because they'd have to contradict your private agreement with the NSA Chief first. if they do refuse, you now have legal recourse in (Secret) courts, because the NSA will now be proven to have obstructed process.