2007 Mazda Truck engine damage

I changed the oil at 3000 miles, that was 9 months ago. I know I screwed up, its been an intense 9 months, I put on my trip counter so that added to the confusion, whenI had a conscious moment I saw that I was at 6000miles, (it was really18000 on the odometer)way late for an oil change. Anyway the engine light came on I pulled over right away, and the dealer says there is no oil in the engine because of a cracked timing belt cover. Verdic no warrenty coverage $7500 damage, no truck. So here's my Question, is it reasonable to assume that because I didn't change the oil for 15000 in a new truck that that would blow the engine. I've bought three cars from this dealer in the last ten years. And I still have an 20005 Mpv with 48000 miles on it. They aren't even considering that it might be something else. I'm going in to make my case tomorrow any advise to help my position. Or am I justup the creek with out a truck. Thanks len