Peugeot 307 engine not working

Car done 72,000 miles, last week went into a dealership and had timing belt replaced, new clutch, full service. Drove home and the bottom plastic tray under the engine fell off (garage apologised and order a new one). I was driving today, still without the tray and the engine went really hot whilst on a motorway, the car said engine coolant too hot. There was a puff of steam I pulled over and the car wouldn't start. I got the car towed back to the original garage which I had just spent over £2k in last week and they have advised that a pipe that connects the front to the back of the engine with coolant has a hole in it and has now caused significant damage to the engine. They cannot get any compression in the engine. I asked whether this could have been affected by the recent work timing belt, clutch, under tray, full service etc... and they have basically said that they haven't been near this pipe and the likely result is that it is going to cost more than the car is worth to get fixed. The question is, would anyone know whether the work they have done is in the vincinty of the pipe from the Rad to the back of the car, as I am sensing that this could well be something else that wasn't completed correctly.

we have owned the car since new and fortunately never had a problem before.

any assistance would be gratefully received.