The guy sent an honest and respectful email asking for help...I don't think his email was unreasonable. What was unreasonable was the "go away" line in David's response. That is simply juvenile and more importantly, completely unnecessary.
Not only can they not be trusted to run the service, but they act unprofessional when you complain. Customers complain, get over it. Learn to deal with it constructively.
David's response is not constructive and William's feedback is very valuable. Period.