Before hanging up did you actually wait for the agent to "try again"? I've had this happen before, the agent will try again or have to call the rate desk and will eventually be able to find the fare if its really available. It just takes a while. If this required calling the rate desk and you weren't willing to wait and HUCA too soon, then it makes sense getting the same response from the next agent. If you did wait and the agent just gave up, then I guess you just had bad luck.