HELP! After oil change engine locked!

1996 Buick LeSabre Limited (mileage 109,839/3.8L V6). We got an oil change on 01/22/07 and afterwards (not exactly sure how long after the oil change) we started noticing engine noises (knocking that got worse). The car eventually stalled on us on 02/22/07. We took it to a mechanic (different place than where we got the oil change) and when they checked the oil there was no oil on the dipstick. When oil was drained it contained large amounts of metal turning the oil silver. There was not an oil leak or anything. The explanation we were given by the mechanic is that they must have not put enough oil, etc. As you can imagine we are having a hard time trying to get reimbursed for this. Here's my question. Looking at the mileage at the time of oil change it was 109,176 (not sure how accurate that is but that's what's on the work order from the oil change). Car stalled at 109,839. 663 miles after the fact. Is it possible/logical for a car to go that long with low oil? Trying to find out how I can prove that the engine locked due to their negligence. Any advice will be greatly appreciated!