Good advice needed. engine seized whilst at garage

[dopeman1979]

So here's the story, will try to be as short as possible
on the 5th I was involved in a small accident, not my fault, someone drove into me from behind, not a big issue, rear bumper damaged, car is a Passat B6 07reg estate. 2.0tdi
phoned the insurance company and they arranged the car to be dropped off on the 16th at TrustFord for repair.
Drove there and dropped the car off, done an inspection to both my vehicle and the courtesy car, signed forms and left my car outside reception and drove with the other one away.
Whilst my car was inspected engine was running, mileage was written down and other defects have been highlighted on the form. (had a scratch on the left front wing ) also was advised that my courtesy car is a petrol one and i told them that my one is a diesel... if it matters.
TrustFord has an online thing where you can check the progress of your vehicle and i was happy to see that the car was approved for repairing by the insurance technician and also could see photos of the highlighted damages and i noticed that the car was in a different place, again, if it matters. got a phone call later that day, on the 18th and it was explained to me what will happen to the car, what parts will be repaired and what will be changed. I said, OK, good to see professionals...
on the 20th i got another phone call and was advised than on Monday the 23rd, as today, i will be able to pick the car up and return the courtesy one.
Around 11 while i was at the car wash, i received a phone call and was informed that my car is ready, just a small issue, it doesnt start but they will look into it. got a phone call later telling me that "low oil pressure " message appears on dash and engine wont turn but this is a common fault with Vw passat and its caused by a sump pipe and that it was due to wear and tear and that i should pick my car up and take it for repair....Also been advised that all fluid levels been checked and they were ok and they scanned the ECU and its not an electrical fault but mechanical but this a common fault at this engine. bla bla bla
I know what u all gonna say, oil pump failure. But, and here is the But...
Last december, 15k ago, oilpump has been changed with the upgraded one and turbo was changed also to a brand new one and i service the car every 5-6k with quality parts and car was driving perfectly.
Garage is refusing to take any responsibility for the existing condition and i am more than disgusted with their attitude.
what i done so far... i refused to pick the car up and called the insurance company and explain the situation and short answer was that they are going to send out someone to asses this matter.
now, if anyone been in a similar situation or has some good advice i am all ears. thanks