Take day off and go their office in KL.
Alternatively use moneymatch. More expensive than instarem.
Another choice use Transferwise. Heard they have account to transfer to SG already but not sure who's cheaper. Instarem or transferwise
That's the only way.

funded my CIMB FASTSAVER account, was told by CIMB SG customer service subjected to their management decision and need wait 5-7 days 

why me la aiyor, i saw others open get activation code less than 2 days.
good things about CIMB is no inward remittance charge, so I
- dont need charged S$10 whenever withdraw from IB
- dont need charged S$10 whenever fund SG bank account using instarem?

Maybank iSavvy has this S$10 inward remittance, quite painful for Malaysian tbh

And álso Priority Banking, Premier Banking, CitiGold, Preferred Banking way and the lowest so far is you lend the bank SGD200,000.

Correction. DBS is the only pure SG bank which allow Malaysians to open account.

CIMB FastSaver is a pure online account, as far as I know there won't be any physical ATM card issued to you. It only allows the Sg account to be an intermediary account for transactions into Sg.
So if you would like to withdraw money from FastSaver, I'm afraid the only way is to convert your money back into MYR and withdraw in Malaysia.

But if you want to have the convenience of withdrawing your cash in Singapore, you can try open a Maybank iSavvy account.
I opened mine without any hassle and they approved my account promptly (about 1 week) and sent me my SG Maybank Debit Card.
With this account I can go withdraw or swipe my debit card in Sg as much as I want. I don't have to even transfer my money back to Malaysia.
This is the account that I will use to diversify my portfolio in foreign currency and preserve the value of my cash, in case MYR depreciates badly due to whatever reason.