I thought SQ was operating the SIN-IST route with refitted B777-200ER with fully flat seats. There was a discussion precisely about this a few weeks ago in the SQ General Forum. Sharing couple of links from the discussion thread, hope they work,
https://www.flyertalk.com/forum/29435416-post1821.html
https://www.flyertalk.com/forum/29437070-post1824.html
Would you mind sharing what day did you fly / aircraft type?