OP, prior to installing a new turbo, the shop needs to do a complete engine flush to get out all of the old/bad oil that is most likely contaminated from the blown turbos. You need your engine, IC, air intake, and the coolant and oil lines to the turbo to be all flushed out. They also need to remove the oil pan and clean that out. That's probably why you blew your second turbo because the shop didn't do a proper engine flush.