Financed car turns out to be a repair trap - what next? (Ford Focus MK4, 156,000 km)

Hello, I need your advice. In 2025 I financed a Ford Focus MK4 1.5 EcoBlue automatic (EZ 12/2020, 136,000 km) from a dealer for 12,000 euros plus interest. Unfortunately, this purchase later turned out to be a mistake. After an accident in which a tension belt from a vehicle in front damaged my car, the expert found that the previous damage had clearly been repaired. At the time of purchase and in the purchase contract there was only mention of a small repainting