Bad Service

Bought a car three months ago. Car gave problems from day one. Won't even go into the problems. Car went back for so called repairs, came back and a few days later all the **** started again. Was told services were up to date and suddenly there is no service book. Asked on numerous occasions for roadworthy certificate and still waiting. Now they have a cheek to go to Seesa who is helping them against us cause we wrote a letter to the bank saying we want to cancel the deal. How do you deal with lying thieving people who just treat you like dirt.