So did they remove the oil pan and pushed all the sludge out the block? If they did and the smoke is less, how long ago did they do the repair? You may just need to drive for a few more days to burn off the oil residual in the cat. If it is still smoking does it only do it at start up while warming up? If it does and smoke is blue, you could have some leaking valve stem seals. Also have the turbo checked for an internal oil leak.