If prices had gone up would you be willing to call EK and be offering payment for the fare difference? Don't think so.
I'm assuming the cheaper fare either already existed (but seats in that fare bucket were not available) or it was promoted recently. In either case there is nothing you can do.

Well except that if the ticket conditions that you have now allow for free/small fee cancellation, then cancel and book again. Just be wary of the flex/saver and max validity conditions of the new fare.