Flipkart Mivi - Product under warranty but not getting refund or repair

i purchased Mivi made Collar Classic with Fast charging headphone-set through Flipkart just few month back in July ****. This is under warranty for one year. * months gone smoothly but now days this head set is not working properly as its battery discharge very soon and its being working for hardly **-** minutes even after its recharge for *-* hours of time. This issue i explained to Mivi and Flipkart on phone call and by written mail , but they would only commit me that issue will resolve soon and this is i am doing since last ** days. But till the date there is no any positive action taken yet. I sent the invoice copy of purchase by mail also. And since last ** days i am pushing every day this issue by mail and cell call .