Engine knocked and service provider denise responsibility

Engine knocked after the car received a major service and work was done on the front suspension by a Toyota specialist garage. Check engine light has always been on and they assured me its just worn out sensors. Major service was done, used car for 4 weeks, it went in for front suspension, used car for one week then engine knocks. Total time is six weeks. They keep telling me I drove car without oil. How can I prove that its there respnsibility to fix my car because I should at least received a vehicle report after service, but they claimed it was not important since they couldnt do it because engine sensors are not working.