Sumatra, Realfish and others. I lived in Singapore for ten years and was an employee of SIA. As with all problems concerning major companies, be it Singapore or anywhere else in the world, you must write to the top, a personal letter sent via registered post to the CEO setting out your dissatisfaction as straight facts, don't get dramatic, don't go over the top just let it be known that you are good customers and you are not happy.
The CEO is Mr Chew Choon Seng and his address is:
Airline House, 25 Airline Rd.
819829 Singapore.
The CEO may not read your letter himself but his PA certainly will and it will be passed rapidly to the Director concerned who will start chewing those below him in his department. It is always better to start at the top and work down, starting at the bottom you are dealing with people who won't make decisions but don't want to be seen to be inefficient etc. so difficult letters etc. just get hidden or passed around the juniors in the office. Best of luck.