In case anyone else finds this thread via a search, I want to update.

The $250 was charged to my credit card and at that time I called back. The agent I spoke to was very helpful and put me on hold while she "looked into it". She mentioned that there were pictures that showed what could be ashes, but couldn't be sure. Most importantly, the odometer was off by 3 miles from what it was when I returned the car. Because of that she said it could have been an employee that moved the car so there was no way to show it was actually us that caused the smoke odor or ashes.

The $250 was refunded to my credit card without much of a fuss. So if this happens to anyone else, ask to see the pictures, and ask for the odometer readings!