LEASING A CAR... INVOLVED IN A SCAM! HELP!?

I leased a 2007 infiniti g35 in 2007. my lease is up next month. the check engine light came on a few weeks ago, and I called the dealer so that I could drop it off because its under warranty. About a week before that I had had my oil changed. When they inspected the car they called me and said I had no oil in the car, and that when they went to put oil in it it started smoking and the nthe engine got ruined. I have my receipt from my oil change the week before, and they said they wanted the receipts to all the times i had to car maintainanced. I have all my inspection reports, and all my receipts from new tires, brakes, etc, but i dont have my old oil change receipts besides the most recent one. I had to call consumer affairs and get them involved. They are trying to make me liable for a new engine when the car goes back next month and I have maintained it for 3 years. This is just wrong and I need advice on how to go about this. They are trying to rip off and scam a 24 year old woman and its wrong!!!