Bad experience

My experience was very bad. Took my Mercedes-benz for chain replacement and service, within 4 days engine light was on, car was complaining oil, car was very slow, when I slow down accelertor would shake, when I take off car would make roaring noise, it just became different. I phoned and took the car back left it there for a day. When I came back was told that catalytic converter was missing and I was like how because when I brought the car everything was fine, the guy showed me what'sapp group where they discuss that catalytic converters get ****** at workshops. They took advantage that I'm a woman probably do not know about cars yet I know about my car. So my car got messed up like that.