Non payment of service fees

This company came to me being a recruitment agent and was looking for a Bookkeeper and a Receptionist. I sent about 5 CV's and candidates were interviewed and finally a decision was made to appoint a Bookkeeper. The candidate started working. I sent my invoice for payment and now this company refuses to pay my fees. I received a letter from them that I am wasting their time and they do not want anything further to do with me. Even though I sent them Terms & Conditions regarding payment they still refuse to pay my invoice I find it very unprofessional and would like to warm other service providers to be aware of this company