Your issue maybe abit different from mine which I faced previously.
1. I did not get my interest after 6 months despite having instruction 2 chosen, so I asked my RM why. She gave some excuse saying they have some internal instruction that interest will only be paid upon maturity.
2. Then I called the hotline about the same issue & complained. It routed back to the RM & she was quite angry saying why I didn't contact her directly. Apparently the hotline officer contacted her & scolded her. But the final outcome still the same, she even said asked branch manager if the 'instruction' can be changed but cannot.
3. Finally, after around a month seeing most of the people here getting their interest paid, I complained on their Facebook page & try to viral it

I got my interest within a few working days no excuses given!

Sometimes I guess it needs humiliation for these big bullies to take proper action.
I see Citibank credit cards Facebook page is also badly defaced with lots of complaints since they are probably the only bank that still do not give annual fee waiver. But when came my turn, they seemed better & said I need to spend a certain amount to waive it.
U guys have so much problem with SCB.
So far the 6 mth interest only have slight problem which was resolved quickly through the RM. Subsequently no more issues. Just received one last week. Also changed Renewal Instruction within one day (showed up online).
OT. CB Citigold free Platinum card. Have been using it as main credit card for years.