I regulary pick up cars where the mileage on the odometer does not match what is printed on the rental agreement. the variance has been as small as 10 miles and as great as 3000. I also have my American Express card set to notify me when transactions are made without my card present. This happens instantly when this opens a contract. When you didn't pick up the car maybe a lazy employee didn't close the contract

I am sure nobody drove the car. Your problem with the mileage was probably caused by lazy or careless employees.

TW