If Du made it than only DU can change it. If your convinced that your agent is not working in your best interest, then you will need to cancel with them and try to book the discount rate yourself.
My DU agent, Carole, sent out an email for all of her clients about the new codes, letting us know that she would try to get discounts and to let her know how flexable you were in your dates to get maximum savings.
I didn't need it as she had got the email rate applied to my ressie earlier, and this new code is for the same rates.
I've beed pleased with DU so far. Hang in there, I'm sure that your agent will come thru for you.