An "irate customers" time isn't free either. Plenty of reasons why one might take the time to write a complaint but decline the opportunity to provide free consultation in person.
The company should be grateful for whatever "help" (or pointers to improvement) they can get - even if it's just a letter - way more preferable than a rant on the phone or slating on social media.
Also: Paul may simply not have been the right person to be there because he's too far removed from the floor to make a meaningful contribution. Delegation to the right person in the org is the hallmark of a good manager.