I had this issue, new crush washer didn’t help so I just used some of that Teflon tape on the threads. 5k miles and no leaks, time to do it all again

Take the intercooler and down pipe off, they’re pretty easy to do. Look up into the intercooler and see if there’s any oil and that’ll tell you if the turbo blew up bad, and if there’s no oil check the back of the turbo that’s been exposed to see if it turns freely

Read up on mechanic laws in your area, that shop might owe you all your money back