Problem is that the coolant pump on the twincharger is combined with this magnetic clutch twopulleys sticked together.
Happens to a lot of tsi's is that the clutch goes bad. When it goes bad the pulley for the supercharger is not locked and the supercharger does not work when needed thus making the car rev very slowly till 3500rpm (limp mode) after this the car is turbocharged but the air flows through the not working charger blades thus slowing the air intake in to the turbo making the car less powerful up to the end.
Hope this helps its from my brother who works for vw, he said that they had problems with the turbos is it under warranty?