Singapore Airlines (SIA) doesn't seem to have a public-facing physical office in Düsseldorf their primary German presence is a contact center in Frankfurt, but you can book flights to DUS, manage bookings, and get support via their Singapore Airlines website or by calling their German Contact Centre at +1-866-829-1086, available weekdays 8 am - 6 pm for reservations and KrisFlyer. For direct assistance, use their Help Centre online. Jauntlet.comhttps://jauntlet.com/