TTS will not go into gear with engine running

Hi just had a call from my son who has broken down. He came up to a roundabout tried to put the car into gear and no chance. He could not engage any gear while the engine is running. Turn the engine off and gears will engage but if gear is engaged the car will jump forward with the clutch pressed down if you try to start the car. The car has just had a new clutch, dmf and slave cylinder.
Any ideas what has gone wrong as he has just called Audi Assist.

I just don't know as everything down in the clutch area is only about 6 weeks old and maybe 2K miles max.
Hoping it is the master cylinder as that should be covered with Audi. Clutch was fitted 80 miles away - nightmare!