Quick update:

SIA have called me and apologized for the trouble and we're friends again.

As for the advice about travel agencies etc. I have one, but this trip was booked by my elderly parents who only fly SIA twice a year to/from Phuket. They always book directly through the PPS system, which until this incident has worked perfectly.

We normally talk to their Zurich office, but they weren't open due to the time differences. This was the first time I spoke to Singapore and they acknowledged that things didn't go as they should've that day.