Please, for the safety and security of your own customers, STOP ASKING PEOPLE FOR THEIR PHONE NUMBERS TO CALL THEM. Just knock if off; it's embarrassing. There's NO WAY for a bank customer to verify that the caller is actually an OCBC employee acting in an official capacity and using a bank-monitored/supervised channel when you do this.
There are only two basic options for voice communications with reasonable confidence both parties can trust each other enough:
1. Ask your customer to call OCBC at the telephone number listed on your public Web site. You can provide a reference code if you wish. Example:
You may contact us by telephone at 6363 3333. You can verify that this is our telephone number by visiting our Web site:
https://www.ocbc.com/personal-banking/contact-us
Please mention reference code ATM1 for faster service.
2. This alternative approach (hypothetical, but it's something you should implement if you don't have it):
Or if you'd like us to call you, please visit:
https://www.ocbc.com/callback
Or tap the "Callback" button in the OCBC Mobile app. Fill in the short callback form, and click Submit. You'll then see a unique, one-time reference code. Do not share this one-time reference code with anyone. An OCBC representative will call you within 10 minutes and must mention this unique reference code to you. If the representative does not provide the correct reference code, tries to ask you for this reference code, or does not call within 10 minutes, you should not trust anyone calling who claims to be from OCBC.
That's it. Those are your only two basic options to protect the safety and security of your customers -- and the safety and security of OCBC Bank itself -- for voice communications.