Paytm Mall - Defective product sold twice

I purchased audiotechnica ath m **x headphones worth **,*** from paytm on ** DEC **** and were delivered on ** DEC **** . Upon opening the product box itself there were two invoices inside(PAYTMMALL ORDER ID :********** AND **********)and on checking the headphones it was defective (right earpiece wasn't working). So, I requested for replacement which was denied because as per paytm policy they only replace physically damaged or wrong product delivered. So, I wa told to wait for two days and they will look into it and I waited for two days and then I called them again as there was no response from them and upon calling them they denied that I did tell them about two invoices and told me that two invoices might be due to a mistake . So, I called them again and asked for details of order Id ********** (not mine) and they told me that it was ordered on ** SEP **** and was returned by the buyer because it was defective . Now, instead of giving that product for repair or replacement to manufacturer or seller they sold it to me and now they are telling me that it is my responsibility to get it replaced or repaired . WHY? I want refund or replacement done by paytm itself .