Amazon India - Regarding non refund of courier charges by amazon

I purchased an exercise cycle for old parents RS ****/- from Amazon India on * aug ** a faulty product delivered by seller, I was asked to send it back to warehouse at Ludhiana and cost of carriage wud be refunded to me.since they don't have pickup service at my residence location.we tried best to get it back but due to wt ** kg indian postal service refused to pick and blue dart asked es **** as courier charges.
Then we managed to send it back thru Gati who took RS ****/_ charges of delivery.
Amazon received the product back which was reflected on my Amazon acct.but despite of their commitment they r not refunding courier charges to me. On repeated calling they asking me to get amount in Amazon pay balance which is like forcing me to buy something else for that much amount which due to their highheaded attitude I am not willing to.