USBank Not allowing me to make another End of Lease offer - What to do?

To make a long story short - I made an offer; and they rejected it. Now they are telling me - this is the price and that's all. They are not allowing me to make a counter offer telling me I was only allowed to make one offer and once rejected - the only option is to accept their offer (which is not low enough - 15.5K all inclusive for 2014 Base with Safety 1 with 35.5K miles).

Is this true based on your experience? Or should I call again and talk to a different person?

Thanks in advance.