"Our review found that the actual price of the advertised fare was never clearly stated during the booking process, thereby creating ambiguous circumstances in which it could be reasonably interpreted that the actual price of the fare was significantly more than the amount consumers paid at the time they attempted to purchase the fare, e.g., $40 plus 4 frequent flyer miles. Therefore, we are not able to establish that consumers, in fact, paid the full amount of the offered fare at the time of purchase."
This isn't true. There may have been conflicting information displayed on the website during the purchase, but there was, in fact, a point in the purchase where the "4 miles" price was displayed. DOT's explanation seems to imply that consumers were never actually offered the 4-mile fare, just that their balances were mistakenly "charged" only 4 miles.