My client is not paying me ..pls help

I have a recruitment consultancy. One of my client is refusing to pay me my consultancy charges.We have sent many reminders. But there had been no reponse from their end. They have stopped talking my call n saying that my placed candidate hv absonded n hence i shall not be paid. We have crossed checked with the candidate and he is still working there. He too has joined hands with the managment n telling lies that he has quit. Pls help what shall be my next move.