What I'd recommend you do is take it apart yourself, but videotape you doing so. Record every angle of it! That way any mechanic can testify in court, and does not need prior viewing of the turbo. (mechanic will probably charge you to do so...)
I remember you said could a turbocharger be harmed by high heat... I doubt it. But if they didnt use the proper oil, bingo. Try to document what type of oil they used, and check of its turbocharger grade, which I think is C- something. I don't know what they put in these oils but somehow they work way better than conventional oils to lubricate the turbocharger. Did they change the oil though? I forget what kind of job they did to your car.. but I'm guessing they did change the oil (its easy enough to do in a garage)
Or... they tried to re-use the oil, or did not change the oil at all... at that point its totally they're fault since turbocharged engines need more oilchanges (wouldnt it be nice if the oil lubricating the turbocharger was separate from the engine oil???
could make the oil run through the engine somehow i'm sure...). If this is the case then perhaps something got into the turbocharger somehow (past the oil filter... somehow....) and wrecked it.
Whats the temperature a turbocharger reaches??? If its around 900C or so then I could understand why turbocharged engines need different oil... otherwise the oil lubricating it might burn if the seals are worn and there is shaft play??? I'm just a newbie when it comes to this kinda stuff
Really hope you get this issue resolved! They charge an arm and a leg, for excellent service, not something you'd expect from doing it yourself!