hi there, i'm a new member but know a little bit about galaxy tdi's. with the cam belt snapping it will have caused damage on a rotation of the camshaft there is always a couple of valves open different ones at different points and with the camshaft not turning and the crankshaft (with pistons attached) turning the pistons have hit the open valves and will have bent them or snapped them off which with the latter will have damaged that particular piston at the very least it'll need the cylinder head removing before anything else to assess damage hope this helps