You cannot pay your HDFC credit card bill through your SBI credit card as it can be paid only through a bank account or through internet banking. If you are unable to make the payment, one option would be to do a balance transfer as this can save you some money if the other lender offers a lower interest rate than the current credit card lender. Another option would be to call the HDFC customer care centre and ask them to convert your balance amount to be paid into a 3 or 6-month EMI.