We buy cars are *****

I bought a car from We Buy Cars on the 06th March 2021. The sales consultant went through the Dekra Report and told me the only faults were the hand brake and faulty airbag nothing about any engine issues. On the drive home from buying the car the engine warning light came on and the very next day I started having issues with the gears its an automatic car . I reported the this with we buy cars and was told to lodge a formal complaint after a week I was told that I signed th dekra report so there's nothing they can do. This is so unfair I should have been warned about this the least they can do is fix whats wrong with the car why would I take out money to buy a broken car.