SQ flies to many countries but its infrastructure are Singapore-based, especially in terms of Krisflyer. Same for almost all airlines as much as they claim that they are global.

for people in Singapore, they can always go to Ion and fix it in person. FWIW, we hardly deal with call center people as we know how useless and random those people are if any problem is out of ordinary. and speaking of that, I am going there today to fix my tickets.