Had this happen to me. I got the same old BS story that I paid for an economy fare that was instantly upgraded to F and since they needed my F seat I was first to be downgraded. Ridiculous BS if you ask me. When I book on Delta I request the F cabin and F pricing and I choose the fare code under the First Class column. Yet they keep claiming this is an economy fare. How is anybody supposed to know this and how does one buy an actual F fare then?