Has the fllight been booked? Taking a deposit for airfare isn't commonly done, most tickets need to be paid for in full within 24h of making a booking (there are a few exceptions but generally not for deeply discounted fares).
If the flights were booked and you had agreed to purchase non-refundable tiickets then you've got a booking to KTM.
Bucket shops may show the lowest fare available for a flight; if there is one seat that may be sold at that fare then the sign in the shop window can show 'From £XXX' and be accurate, even though most people will find a higher fare when booking.
That's why as npj60 said, it's usually recommended to book with the airline, as the most up to date fares will be available directly from the carrier. Booking with the airline usually won't attract fees as high as those charged by seabreezeholidays.com either: http://www.flighthouseuk.com/