I'm also taking OCBC loan. Whenever you pay extra, it will be automatically treated as "advance instalment" and cannot be withdrawn.
This is like you pay in advance for the monthly instalment in the future.

Don't worry though, because this extra payment will immediately save you interest. You can check your daily interest to confirm this.

Another type is "capital repayment", this can only be done through cheque deposit or over the branch counter. This will also immediately save you interest, but you can withdraw this by giving OCBC 3-day notice (minimum withdrawal amount 5k, and increments of 1k for my case).

Either way, you save the same amount of interest 

Just a note, in online statement, your outstanding balance = total balance - accrued interest

for daily interest, you have to do ur own calculation.
the accrued interest will increase daily, u need to calculate the difference to get the daily interest.

interest become bigger? now that's strange, I think could be due to the raising of BLR?

that's why you must make principal repayment whenever it is possible (e.g. bonus, income from other ventures etc). to reduce the interest amount. FYI, if you pay the installment without making any capital repayment, the total money been paid for interest is as much as the amount of your principal amount.