thanks for the prompt replies guys, so whatever they double charged ive to pay 1st, then they revert back? oh god i hate to call the bank, pass here pass there like Barcelona FC

actually this depend on whether the mistake on bank or merchant..
if bank mistakenly double posting, they could reverse for you.
however, if merchant doublel charge you, you need to go back to merchant to void one of the transaction.

good luck to you 

i just called the maybank guy. he said similar thing. he said he will open a report, but to expedite matter, he suggested i also talk to the merchant . at the meantime, they will investigate and etc. Now i am confused who gonna pay me back that money lol, and in what form? 

I <3 M2C Cashback Campaign
Campaign period: 22 September 2014 -22 March 2015

Swipe each of your new Maybank 2 Cards 3 times and enjoy RM100 Cashback.

Terms and Conditions:
- Campaign period is from 22 September 2014 till 22 March 2015.
- The Campaign is applicable to "New-to-Bank" or New Principal Maybank Cards or American Express Cardmembers whose card is approved and activated within 60 days.
- New Maybank 2 Cards Cardmembers are required to apply and to spend 3 times with any amount on each card to be eligible for the RM50 Cashback on each card within 60 days.

Source: Maybank | T&Cs

btw whats  " i love m2c cashback" ?