WA Brought faulty used car from dealership. What can i do

[KaraniPani]

I got a car from local car dealer for $3500 on 26/5/2017. When i saw the ad it said it was mechanically sound and had been serviced. Since having it i have had problems with it. Took it back to dealership and told him what is going on. He told me to take it to the Mechanic that he goes though. I have been to them twice and have been told two different false diagnosis that they thought was wrong with the car first i was told it was the fuel i was using and told to change it to 95 instead of 91. The second time i was told that it was th inlet manifold. And it was not. A friend who is a mechanic. He checked the engine compression cylinder 1 is 150psi, 2 150psi, 3 & 4 50psi (not working). Two blowen valves. I have been running on 2 cylinders instead of four. I have bearly driven the car and now it is not drivable. Only time i drive it is when i went to the dealership and mechanics. What can i do about it.