Nice work keeping the paperwork on this case. Even a handwritten note from an employee is enough to cast doubt on a $600 repair bill sent to you long after you returned your rental.
If Thrifty had a legitimate claim – and I’m not saying that it didn’t – there was a right way to handle it. The company should have asked you to acknowledge the damage by filling out a report. You didn’t fill out a report; instead, both you and an employee documented the fact that the car broke down.
Since Thrifty had already punted your complaint to its Cancún location, I thought a better strategy might be to contact American Express to dispute your charge. Although merchants can retroactively charge you for items (called a “late billing” in the trade) they also have to provide adequate documentation. I thought Amex might want to have a look at the paperwork.
I contacted American Express on your behalf, and it reversed the $600 charge.