Your credit available is confusing, it is RM 300.++ or RM 3000.++?
If it is only RM 300.++ (three hundred plus), you cannot but if it is RM 3000.++ (three thousand plus) then you can buy.

By this I assume your "2100++" means RM 2.1k+ (two thousand plus).

If your credit limit is insufficient and you really want to buy that item, you have the below choices:
i) Clear your outstanding bills to ensure sufficient amount for your item.
ii) Top up your credit limit by cash, i.e. pay via CDM, IBG from other bank
iii) Call to bank for temporary credit limit increase but this is very tough unless you have a proper justification, like due to emergency in overseas, pay hospital bills and etc.