It is our sincere regret that you are not able to enjoy our First Class, and I would like to ask for your understanding that unscheduled aircraft change sometimes happen and thus operating class changes.
In terms of air fare, Star RTW (Round The World) ticket fare is based on the highest class booked- in your case First Class. Even though First Class is not available for all segments, if any segment includes First Class, the fare is calculated based on First Class the highest class booked. However, it is designed to be still cheaper than issuing individual lower level ticket. If First Class is not available for any reason (ex. overbooked or only two class served), next lower class is provided and the fare remains the same.
Thus it is true that base on the Star Alliance RTW fare rules, the fare you paid does not change even though the class has been downgraded. However, because you were inconvenienced due to unexpected downgrade, as an evidence of our concern, we would like to provide Asiana Airlines Travel Credit Voucher (TCV) worth $300 for the downgrade for two flights. Currently in Asiana, we provide TCV worth $150 for the passenger who was downgraded from First to Business Class for the flight hour less than 4 hours.
TCV is valid for three years and can be used for services provided by Asiana Airlines - air tickets, excess baggage charge, in-flight duty-free items, etc. Please kindly let us know if you are willing to accept them and if so, please let us know your address we can mail the TCV to.
Once again, we apologize for the inconvenience and ask for your kind understanding for the unfortunate situation. Thank you for flying with Star Alliance and with Asiana Airlines.