VAG 1,9 TDi engine blew up in my mothers Seat

[Skaala]

My mom had her Seat Alahambra 1,9TDi 115hp (148hp chip) in for a service a couple a weeks ago. They where to change the timing chain/camshaft belt, and changine the oil filter, oil, etc. Main thing was the chain. After my dad picked it up, he noticed a ticking sound from the engine, sounding like problems with the valves. So he calles the garage, and they assured him this was normal right after a change. He thought this was wierd and all though he has a lot of technical competence he called me, and my uncle discussing this.

Laster the next day, my dad,mom and granmother was driving for our cabin, and in the middle of nowhere on the haukeli mountains the engine suddenly lost all power, and the engine completely went out with a bang. This was in -25 degrees celcius and they had to wait for 2 hrs for a tow truck and rental car.

Back home the repair shop said that, well actually to cut it short they said "shit happens" The top was completely broken, the valves and hydraulic lifters were smashed flat, the cam was broken, and 2 cylinders had to be changed. Meaning big $$. They also completely rejected that their mechanic could have for example set the timing chain wrong. (barely accepting they were notified of the wierd ticking sound)

We got hold of all the broken parts and sendt them in for analasys, hoping they could tell us what happened. So far they could not 100% say what was wrong. Only thing that is certain is that the car was purring like a cat when it was delivered at the shop and blew up shortly after service...

The engine is a 1999mod at 160.000km

Any thoughts on what might have caused it?