1998 Vauxhall Vectra Engine Seizure

Hi,
I bought a used car from a dealer and within less than a week, the car overheated and the engine seized. I was driving down a bypass which is a no stopping zone, when I noticed I couldn't accelerate past 40mph. Suddenly the oil light came on, then the engine management light and the battery light, and then within 1 minute, the car completely shut down. I have taken it back to the dealer, who said a burst pipe caused the cooling water to escape, causing the engine to seize up. They are saying that it is due to my negligence in not stopping, despite stopping at my earliest convenience, has caused the engine to seize and that they are not responsible. I dont know much about cars, but surely the pipe must have been faulty when sold and also something wrong with the car as it overheated for the pipe to explode. I just need to know if it is my fault or an underlying fault with the car, so I can seek legal advice and claim my money back.

Cheers,

Craig Williams