FYI, I hold titanium, 3 platinum & 3 visa signature with the recent one from HSBC which is known hard to get. However, I did apply for MBB Dual for 3 times for the past years and all are rejected.  My company current account is also with them for more than 7 years with healthy records. Sometime it is hard to understand how bankers evaluate us.

Since OCBC rejected you, why don't give a try at others bank since your income is eligible for it. There are many banks offer cash rebate card too such as HLB Wise, Alliance You:nique and Citibank Cash Back. Study your spending pattern and hunt for the right card that suit you. By the way, you must also have a clean CCRIS and CTOS record in order to get your application approved. As far as I understand in CCRIS record, any number 3 will have 0% chances  while any number 2 is 20%  and any number 1 will have 50% chances  in you application approval.

Wish you all the best and good luck in hunting your new card.