Enterprise Rental Car Compnay THE ENGINE BLEW? Upper Darby, Pennsylvania

On May 04th 2012, I was driving a car I rented from Enterprise when the car just stopped? I called my tow company and they towed the car to Goodyear, which takes care of the mechanics for Enterprise in that area? Enterprise came to pick me up from Goodyear. When I got to the office, they told me that the car didnt have any oil? I didnt understand what that had to do with me, being as though this is a rental car and not my car? The manager stated because I dropped their insurance and was using my AMEX insurance that the car was not covered and I may owe them for the damages? I didnt understand what any of that had to with me? He asked me did I get the oil change they asked me to get a week and half prior? I said, no becasue I'm bust and honestly its not my responsibility and a car should have not seized in a week, if I didnt get the oil change? I was told by one of the workers that they should have not re-rented me the car becasue it needed an oil change, however they still rented me the car and this is the result.  I was told later on that day after I left that, the oil pan was broken and the oil leaked out and that's what caused the oil to drip out? I was given 3 different stories on why there was no oil in the car. The last story I was told, was that and oil change was done and the oil filter was not done properly and that's what caused the engine to seize? Then I was I put a claim in with my credit card company and they paid the deductible of $500.00. Then on June 05th, Enterprise debited $500.00 from my AMEX card? They sent me a bill stating that I owed them 3000+ dollars for the damages doen to the vehicle? 

I am completely at a lost for words with this place? I am NOT paying them back on a bunch of lies and on a rental car? This was their fault and myinsurance company refuses to cover the damages, becasu ethey feel its not my fault....which is true. I was utillizing their insurance, but it was a ri-off, becasue I had the car for about 3 months and the monthly bill was $1,400? The insurance was the same amount the car rental? I refuse to pay this bill and I want to take them to court for this nightmare!