Vistara Airlines — booking not done but money deducted from my account

Hi,
This is regarding my booking i made through my hdfc debit card on 8th may 2018 for a flight 816 vistara. The flight is from bengaluru to delhi.
I made payment of rs.12507 through my debit account, however the flight was not booked and the money was deducted from account. The payment was done through net banking. And i have all the supporting documents and transaction ids.
When contacted the customer care, they said, it's going to take 7 working days for your firm to return the money back.

However, for a person like me, it's very difficult to believe to customer executive saying the same, i asked him to just put an email stating the same if you are very sure that the money will refunded. But the customer executive declined that as well.

The summary is, i am very agitated, the money being so hefty and such responses from your firm's end, shatters all my respect and dignity for the organization. My call was cut in midst leaving me hung up during the conversation of customer executive. Being a defence personnel, i believe that the customer should be answered with all questions and doubts he or she is having, especially in such case when the mistake is from your end. It is difficult for me to i believe the words of your executive when i was hung up in the middle of call.

This is the first time i was booking my flight with vistara. With the unfolding of situations, i think it will definitely be he last one.
Please provide me proper explanation on your part about the money refund.
Asap