Sakhi sew in style boutique - Defective product received

I have received a defective item and when I raised the complaint,they asked to return the item myself and they will send new item. I requested them to reimburse me the courier charges since I have already paid the shipping charges for purchasing the item and receiving a defective product is not my fault. They agreed to refund the amount and I returned the product. Even after a lapse of * month since I have raised the complaint, they have neither send me the new item, nor refunded the courier charges. They are not attending my calls either.