What should I do when the ambulance company ignores my good faith attempts in writing to requst a reduction of the bill and sends it to collection?

My minor son was involved in a car accident while I was out of town and he was taken to the hospital. He was not injured. I am unemployed, do not have health insurance nor automobile medical insurance. I am unable to pay the $1000. The hospital and emergency room physician charges have been substantially reduced because of my circumstances, and I sent all documentation to the ambulance company to substantiate the reduced bills. I also returned a call from the creditor and left a message and never received a call back.