HDFC Bank — Refund awaited for failed transaction.

I made two mobile bill payments from payzapp wallet on 16th august. Both the transaction got failed, money also got deducted. I called their customer care, got a reference number 37047. I also wrote a mail to them and got reference number 36905.in all these cases, i was asked to wait for 5 and 10 working days. Today is 17th working day, still i am waiting for refund of money deducted despite of continuous follow-up with customer care despite of the fact that customer care also accepted failure of transaction. I don't understand what is stopping them to refund my money. Can any one suggest me how to go legally on this? To whom i have to contact?