Does this sound correct? Can anyone clarify/elaborate regarding this matter? It happened after a local repair shop gave me a tune-up. When asked why my car was now sitting and riding this way, the mechanic became hostile and refused to answer. Later another mechanic looked at my car and told me this part was missing but should not be able to just fall off, so someone removed it. What part was he referring to? Help, please!

have taken car back to shop about 10 times they keep putting new clamps on muffler but it will only hold it up for a short time i think its the wrong muffler but they say not