Plaza Toyota

I bought a 2007 certified used car from Plaza Auto Mall on Saturday late afternoon. At the time I drove it home, the car was running fine. But the next morning, when I drove it for 20 minutes, the engine started to overheat. And then 20 minutes later, the engine was extremely hot. I pulled over the car and turned it off. I tried to start it, but the engine was shaking, the whole car was shaking, I can't start the car. I let it cool down a little bit and tried a couple of times, the engine and the car were still shaking. I had to call roadside assistance to tow my car back to dealer. I only drove this car for 2 times, a total of 1 hour on the road, and I only owned this car for less than a day(just overnight). The dealer is still trying to fix it, they denied it's a damaged car and refused to give me a refund. And they threatened me that if I don't take the car back, they will leave my car on the street, if the car is lost, it will be my lose and responsibility.