I suggest take out the letter and read thru the tnc again before getting too jumpy.
My recollection is that there will be 3 times interests will be credited within a mth, as what you have rightly pointed out.
1st time.
End of the mth, they will credit you the interests based on the base interest rates
2nd time.
End of the mth, they will credit you the interests based on the current promotion. E.g. the current promo reference mth is sep. So they will compare oct ADB and nov ADB with sep ADB.
3rd time.
If you are on the one yr promo programme, they will credit you the interests on 20th - 22nd of the following mth. The amt of interest depends on the ADB of the mth comparing to the ADB of the mth you joined the promo minus the interests given at end of the mth.
E.g. on 20th sep, the interests received = interests (ADB aug - ADB mth joined) - interests (collected in end aug)
In your case, did you receive any interests on 20th sep?
If yes, does the interests on 20th sep + interests at end aug = the interests you expect?
No leh. I joined the extension in Mar 2019 (I think cos I know my 1-year extension runs out end of March 2020). So I also assumed that my comparison month would be fixed at the month when I transferred my funds in.
For 1 or 2 cycles after joining extension, things were fine cos I unknowingly maintained ADB. I would receive 3 tranches of interest every month, 1 around 20th of the month and 2 on the last day of the month.
But in August I only received 1 tranche at the end of the month. When I called to ask why, CSO said it was because my ADB for Aug was lower than ADB for comparison month which was July.
Any bro can confirm? Cos if what Squaredot said is correct, I've got a case and I wanna demand my interest back