Lengthy calls to united could not locate the original itinerary using my confirmation code, eTicket number or CC used to book the flight. The agents said that United Customer Care does not have a phone number. Does anyone know if they do?

The situation:
I book non-refundable flight and receive confirmation. About 1-1.5 weeks before the flight I cancel my reservation over the phone and receive an electronic travel certificate pin number for the $900 cost of the flight that is good for 1 year (subject to a change fee for booking a new flight). I have since lost the pin number united gave me.