Defending your self procuring cause

I have just completed a mediation hearing a broker is saying she is the procuring cause of a sale that I have completed. I have letters from the unhappy buyers that wouldn’t work with the agent from her brokerage. The house was quiet expensive. The selling price was $755.00 the mediator wanted me to pay her 2 1/2 % she his demanding. How do I defend myself didn’t go to arbitration yet. I don’t have money to pay the broker that money. What r my options