Singapore Airlines (SIA) doesn't appear to have a dedicated physical sales office in Addis Ababa, Ethiopia instead, you book flights to/from Addis Ababa (ADD) via their website, use their online Help Centre for support, or contact their central customer service, as Ethiopian Airlines (ET) often codeshares/operates on routes between ADD and SIN. You can find deals on Skyscanner or Flights From. Jauntlet.comhttps://jauntlet.com/