Misleading & Poor after service

Hi. Seems like I’m not the only one to be **********. I bought a 2010 Mercedes from them with balance of motor plan. Was told to come to them first instead of going directly to Mercedes if there’s any problem. The day I drove home from dealership (Saturday just before closure) I heard a sound like when your tyre goes over something, but my path was clear from any objects or damage to road surface. Upon inspection I realized a chunk of the tyre missing. Immediately tried calling the dealership but it seems they were closed. Called on Monday to inform of problem but was told that the car was fine when I drove off. A week later I went to Mercedes to inspect the squeaky sound on side mirror, coolant indicator despite topping up bottle, faulty hooter and was told to book in the car, I was surprised when service technician at Mercedes informed me that the extended maintenance plan will now be cancelled due to the vehicle being involved in a collision with front impact. It was evident from pipes behind the grill that were bent and after market headlights fitted on. These were not disclosed by the dealership and their manager refused to entertain my requests to fit original headlights or rectify the concern of me being misled. Whilst running a “RMI” workshop, it is a concern that they stated that they themselves were unaware of the vehicle being involved in a collision.