Hi,
That wasn't good at all. It's insane to know that they ask people ridiculous questions spanning years in Nigeria/Africa as to other areas. At the same time we won't blame them 'cos our system is so much bastardised that they never trusted us both home and abroad.
My advice is to just let it go bcos if you check your 1st NL very well , it was categorically stated that the fact that you were selected doesn't mean you'll be issued a visa, so based on that i don't see any court you'll go that you'll be justified.
If i remember correctly, the guy that was called back after refusal did not do anything he was only called back properly after they found out they made a mistake refusing him.
So in order not to waste your time and valuable resources, i advice you not to file any case, it might worsen or jeopardise you future dealings with US. It is not the end of life and so far you're not bound from applying to go to US in future, you're very fine.
That's my advice, i refused to be crucified.
Good Luck.