Netstar trying to Rip me off

I have received a letter £rom Netstar threatening me with legal action. I have send them numerous emails explaining that I do not have a contract with them. I had contract with Budget and Netstar had a contract arrangement Budget. My contract was with Budget and all payments was with b<dget. I cancelled the Budget contract offer last year in May. I never signed any contract with Netstar. I cannot pay for services that I did not sign up for. This is not professional. Your contract was with Budget. The car was sold. So to who were you providing the service to.