Try to contact another sales office in your country instead of the global call center, maybe they will offer a better solution, while I hardly see they will reschedule with another airline they should at least give you a refund. You have all my sympathy, unfortunately Oman Air can be awful in managing such kind of situations. Despite I love their J product and onboard service, the quality of their customer service respond in case problems arise is the main reason I decided not flying them anymore.