not reshipping returned item as well as not refunding my money

I had purchased a shirt from myntra.com . due to some fitting problem i had returned it. they cash backed that money in my myntra cash back account. when I requested them to refund my money in my bank account then they had debit that money from my myntra cash back and also not refunded it my bank account.
then I asked them if you are unable to refund my money in my bank account then you just reship my product what you have received from me as return or re-cash back that amount in my myntra account. then they refusing to do this also.
I just want to say that how can anybody charge me without giving me the product.