2002 Jaguar S-Type Lower inatke manifold

I was in an accident several months ago, and took my car to the shop. I had hit a small curb straight on and in cracked my oil pan and also cracked the steering column, among other smaller things. I had it fixed and went to pick my car up. On the way home the check engine light came on, however the car was running just fine. I called and the mechanic said that they had put gas in on a test drive. I asked if it was premium and he said no. I assumed that's why the light came on. After a few weeks the car began to idle rough, and shut off if I left it idle for more than several minutes. When it was cold it also would hesitate occasionally during acceleration. I assumed I either had a vacuum leak, or needed to replace the plugs. I took the car to the same shop that had finished the work before. They said it was a vacuum leak and would need to take off the upper intake manifold to fix it. I asked if any of this would be covered under my warranty(i don't know if any of the work they did required removing the upper intake manifold), I was told no and it only needed the gasked replaced. When I called to pick up, they said I now needed a radiator hose and new plugs. I also said ok. I called again today to pick it up, and now am being told that all along the problem was a cracked lower intake manifold. I guess I am asking what my course of action should be and am I responsible for the costs, of the mistakes they made trying to figure out what the actual problem was.( That cost being $500) now they want another 1000 dollars to replace the lower intake manifold. Please help.