The repair shop changed my spark plugs when it was the egr valve that needed replaced a week later the plug blew out. I took it back they said they fixed it. It is now smoking when i start it and wont idle

Headlights flicker when car is running. Checked grounds, they are good. New battery. Alternator is good too.. this is most annoying. Also had the 2 little hoses that connect to the exhaust tube blow off, EGR pressure sensor landed on the exhaust tube and melting it, EGR valve blew a chunk out the side of it, ordered new one of those and rhe EGR solenoid as it too melted and landed on the exhaust tube.. why would this all have happened? Could be clogged up CATS? I did get some Cata-Clean.. will put this all together and see if they blow off again.. just looking for some input, if anyone has any it would be appreciated. Thanks