No compression

Towed vehicle to dealer as car was not starting. Tested battery and said it was okay. Removed intake and said they found no compression in front cylinders and air leaking by intake valve number six. (Charged me $440.00 for this diagnosis.) Telling me that I need to have the timing chains replaced or have a new engine put in. Cost: $5,600.00 plus tax or $5,200.00 plus tax. (This is on separate piece of paper titled "timing chain replacement" not mentioned on the invoice.
My problem is this: I already had the timing chains replaced at 82,000 miles as this was a known GM problem and a recall had been issued for "stretched" timing chains. (Now just outside of the extended recall by a few thousand miles and dealer not wanting to do anything for me even though the timing chains were already replaced (supposedly.) And therefore should have held up. My question is this: No compression in all cylinders equals timing chain problem/replacement, but does "no compression in front cylinders and air leaking by intake valve number six equal timing chain/engine replacement? I would like to know if they thoroughly investigated the problem or if there was more they could have done? I asked them why the "timing chain or engine replacement" is not mentioned on their invoice, nor is it mentioned as part of their diagnosis, but they will not answer me. I do not trust them for a lot of different reasons I will not go into.(There has been a lot of contention/issues with how they have dealt with me and this vehicle.) Now, they say they are more than happy to take the vehicle off my hands (and try to sell it at auction) if I do not want to repair it. (It has had a lot of work done to it in recent years-new transmission, new suspension (and the list goes on), and should have had lots of life left in it. It looks great and was well maintained over the years.) If the timing chains were replaced three years ago, they should not be going again. That just makes no sense! Either the work was not done properly, or, it was not done at all!) Either way, I feel like I am being ripped off as none of this would be my responsibility! (The biggest issue I have with all of this, and which makes me question their diagnosis is that 1) The car was running totally fine until it did not start. There were no clues whatsoever that this was about to happen. No "check engine" light, no noise, nothing! (That, to my knowledge is not typical.) Usually there are warning signs with timing chains stretching or breaking. Also, the engine oil was changed regularly even ahead of schedule, in some cases, so it was not poor or sloppy maintenance on my part. So, getting back to the issue. Could it be something else? (Other than the timing chains/engine replacement recommendation?) I would really appreciate a second and unbiased opinion.