Originally Posted by
CALlegacy
If this is indeed such a fare DL gave the ticket holder exactly what was purchased when plane changes happened.
Incorrect. OP purchased (presumably with cash or miles) a seat in F. If it was an UP fare, there are also different types for ATL-STT. In all cases that UP fare costs a premium over the base fare economy seat, so you do pay more to sit up front. It doesn't mean you buy the cheapest economy fare and magically get a ride in F.