Amazon India - Package was returned to amazon but refund was not issued

I ordered belkin wireless mobile charger from amazon but because of the slow charging for the mobile phone , I returned the product back to amazon. However , once the pickup was done by amazon executive , amazon was not ready to issue the refund stating that - A different item has been received at the fulfillment center. Customer needs to return the actual item . This was a complete harrasment for me as If there would have been any change in the product then the amazon courier person should have informed me but he did not. Moreover , If I returned the correct product and it as different at the time of receipt by amazon , Then amazon should check what happened at the time of transit. Why its directly blaming to the customer.