Just tried again - this time they ARE available but.... "...only if you make a seperate booking sir, otherwise they are not bookable.."......are they just making this stuff up? Silly me, of course they are.

Am now waiting for a Supervisor.......
Supervisor finally booked SIN-BKK in J on SQ x 2. Seperate booking & only charged me the taxes ^ All-in-all it took about 2 hours