I-On — Device Refund amount

I had taken service for 6 months. Paid full amount and extra Rs.500 for device which was refundable after I return it.however during the connection period I faced lot problem.slow network. my mobile network was better than their network.i had paid for 60 Mbps but I was getting less than 10 Mbps. After fed up with their service I had returned the device.but they are not refunded my amount.past 6 months Iam communicating with them but they are not replying.they will say we will get back to you in 24 hours. till date they have not called me neither they have responded in email.they willl just forward my email to other team by saying concerned team will solve my problem.