Help me in overcoming the problem in online examination form

well only the guys at ICAI can help you. Email them incase you still havent been able to get through by phone.

also, contact HDFC and get the transaction reference number for the above payment, so that you can quote this in your complaint.

Since this might take time to get resolved, If I was in your place I would fill the form online once again by paying the fees again. logically, they should refund the fees for your initial payment once the matter is settled.

contact with your bank, If it is not you will get the reversal of the ampount. And after confirming from icai make payment again.