How to book a flight knowing farecode
 

I know a farecode of an itinerary that I am interested in booking but its not bookable online. The fare changed as soon as I go from kayak to asiana website.
Is there a way to call the reservations and and ask them to book it if I know the fare code?

Yes, you can call OZ and ask them to book the flight; in MOST (but not all) cases, the first character of the fare code is also the booking class. So you would do well to tell the OZ agent that she should book you in that particular class. After the reservation is complete, ask her to price it. If the price is what you expect it to be, you are home and dry. If higher, tell her that you believe fare code XYZ should price at $ABC, so why does it not in this case and what can you do to get the lower fare?

There are hundreds of factors which may cause a variance, but you should let them work it out. Good luck, since the OZ agents are not the brightest!

Where are you located? Look up the number of Asiana in your country and just call, it can do no harm.

Later Edit:Many possibilities: the seats could have sold out, it may be a different fare class, etc. Kayak always tells you which seller they are quoting. You should pursue it with that seller. Of course, if you want a specific fare class then better use phone; all of the usual vendors have phone reps. But starting with the airline may well be your best bet.

Just don't give anybody any money until you are satisfied about what you are buying. :)

Did you know they don't guarantee their search results? You can alway call and ask OZ reservations by providing fare basis code(s), however, you cannot claim same price just because you saw the price on Kayak.com.