We Bought a defective vehicle and we were not told of the mechanical defect the vehicle has.

We saw a vehicle that we liked on We Buy Cars Midstream 2 weeks back, on the 9th we decided to go and check if the car was still available, we found the car and we checked it out, we went out for a test drive, the was driving fine. We came back and asked if there is anything they can tell us about the car and we were only showed a small dent by the back passenger door which we said it was not a big problem and that was all that we were told. We paid a lot of money for the vehicle with so much trust that the vehicle was okay, we left We Buy Cars around 11 in the morning. Late in the afternoon we drove out of our house and a light popped up, the light was for oil, we immediately drove to the filing station and we put a 500ml pint of oil. The following day we started the car the light popped up again, by the way we had not driven the car for even 90km from the time we took it from We Buy Cars but already the oil light consumption was questionable. We kept topping up oil until we then decided to ask at some garage and they said we should take it to Audi it looks like its a Turbo, we were so puzzled, l mean after paying so much money a Turbo is something big to buy a car without being informed of such. with the frequency of the oil light pops up, there is no way they could not have picked up when they bought the car from the previous owner. My husband called We buy Cars on Tuesday to inform them of the problem the car has and the lady he spoke to advised that we take it to Bosch for thorough checks which Im sure they do before buying the car or when they are pricing it but we were never told. We are booked at Bosch this afternoon but l just couldn't get the whole Bosch thing when its hardly a week since we paid and collected the car from We Buy Cars, by the way the diagnostic fee at Bosch is our reponsibility. SO l decided to cal We Buy Cars again this morning just to get this right and l am told because we did not pay warrant cost that means they do not take responsibility, l mean how is it possible that we were going to know the car we were buying had such a big defect, really a Turbo for an Audi Q5 cost a lot. I am so stressed already with the outcome of the Bosch diagnosis, I just cant think straight right now.