How good is a airline ticket credit if it is hard to use?

Flight Date: 5 June 2012
Airline: United, flights UA258 and UA785

I had a $479 ticket credit, due to a flight that I did not make in August, 2011. I was informed that there would be a $150 change penalty, but that I could book another flight within the year with this credit.

When I made a $320 flight reservation (for a [domestic] flight departing June 2012), my understanding was that with the $150 penalty, the total cost would be covered, with about $9 left over.

Instead, when I received my e-ticket it indicated that the $150 change fee had been charged to my credit card. When I called to report the mistake, I was informed that their policy required them to make this charge, but that I still had a $150 credit for a future flight.

When I asked that the penalty be taken out of the money they already had from me, my request was refused as "against policy." When I requested a waiver to the policy because it creates a financial hardship for me, my request was (quite rudely!) refused. The agent refused to give me his name, other than "John."

This policy seems unfair and unjust--simply a way for the airline to manipulate passengers into booking another flight with them. I believe this policy should be overruled by airline regulators.