I have a 61 plate insignia, I had white smoke coming out of the exhaust and a burning oil smell. Was whistling quite bad too. Took it to a garage and they said it was a turbo replacement needed. So paid £1100 to have it replaced and Dpf cleaned. It was fine for a few days then started smoking again. Took it back and they said it was a faulty turbo,  which they replaced again. It was ok for a few days again, then the smoke came back. oil pressure low comes on the dash, they did an oil pressure test and said it was fine and they can't think of what else it could be. It's whistling quite loud again now. I've got to take it to another garage next week. Not happy as I've spent alot of money to have it fixed. Has anyone else had this problem? 

Sounds like an oil pressure problem. 
Has the oil and filter been changed each time with the turbo replacement?
Also smoking could also be the burning off of accumulated oil in the exhaust