Myntra - Amount debited twice

I have placed an order for * shirts from Myntra online via my mobile app. Executive from Myntra arrived at my place dated ** Nov **** with shirts which I have ordered then I tried to pay him via online some payment gateway(scanner).
The first time when I made the payment my account debited with amount INR **** however, the executive told me that amount was not received at their end and that guy told me that this issue happens not to worry the amount will be credited back to account within *-* business days so after his assurance I went ahead and paid second time with same mode but this time scanner was different and this time payment processed successfully and amount debited with INR ****.
The total amount debited from my account were INR ****(INR **** + INR ****) only for one order.

Later after trying the products the shirts were not comfortable and not what I expected so, I returned both the shirts and got the refunds successfully.

However, regarding the issue for the amount debited twice I called up Myntra customer support and had a conversation with Ms. Swathi(Myntra Executive) I elaborated the scenario she acknowledged and assured that she will look into the matter. Revert to which I provided my bank statement and SMS(Screenshots) for the amount debited and despite of promise they closed the case stating that "we won't be able to help as the order was not place which means myntra team didn't understood my issue and advised me to contact the bank". I asked her shall I dispute the transaction with my bank as I have a schedule to leave out of town but she advised me that won't be required.

I am writing them again and again and trying to reach their customer support team but instead of understanding actual problem they are closing the issue.

Then again I placed a request for call and one of the Myntra's executive(Mr. Sailender) called(Dated ** Dec ****) me and I explained the issue again and he understand and acknowledged the issue that order was placed however, the amount debited twice. Mr. Sailender told me that he will be writing the email asking for bank statement but this time also they continued their poor customer support not wrinting me email and closed the issue stating that they won't be able to help me contact the bank.

I want to file case against them and send the legal notice to all executives whom I had a conversation and Myntra's CEO for the issue which happened with me and mental harrasement Kindly help me with legal procedure.