Timing chain tensioner break

I drive a 2005 Mercury Mariner with about 140,000 miles on it. I recently had the timing chain tensioner break while I was parked (I turned the car on, it was making tons of bad noise, so I turned it off and had it towed to a garage). I got it all repaired including a new timing chain for about $1000. The guys assured me that even though it was an interference engine, that because I hadn't driven it with the tensioner broken, that I would be just fine going ahead and doing the repair, even though the chain was off by at least 3 teeth. After the repair, there was some valve noise there that hadn't been present prior to the tensioner breaking (it was loud enough that I would have noticed). They again assured me that it was no big deal and I should still be able to drive it for a long time. Three weeks later, while I'm driving down the highway, the car completely loses power and dies at the side of the road. I get it towed again and this time am told that the engine is toast. I think they tricked me into the first repair hoping it would work and now are refusing that they did anything wrong by telling me it could be fixed. Did I get screwed or are they right?