Unresponsive and unwilling to take responsibility

Bought a car from the Dome branch and had it inspected straight away by a mechanic, he found the radiator leaking very badly and advised the car was unsafe to drive and needs a new radiator. I contacted we buy cars and sent them a quote as they requested. They have now been giving us the runaround for over a week, extremely unresponsive and not helpful at all. I assume they’re hoping if they just don’t respond we will eventually give up and repair it ourselves which is not going to happen. Selling a car with such a major issue is unacceptable. It came with a spotless Dekra report so either Dekra aren’t doing their job properly or we buy cars are having them look the other way on issues to make it looks like the cars are cleaner than they actually are. We will be taking the matter further legally but in the mean time have been without a car for two weeks.