Why didn't he just call the phone number on the bill?  Banks buy and sell pieces of each other all the time.  Calling "the bank" and hoping to find someone who knows something about your account is incredibly naive.  I guess he needed that kind of naivety to create Dilbert.  Maybe guys like this are able to point out the weird things we've adapted to because they aren't able to adapt themselves.  Seriously, it takes a kind of mad genius to think that a randomly chosen customer service person in MegaCorpBank would have the means to access his account information or even figure out which piece of MegaCorpBank he has an account with.