Airtel DTH - Airtel Black box not working and not resolving and giving back the deposit money

I have taken a Airtel black Xtreem connection on **th sept ** on the promise that if I am not satisfied with the performance / service I will get back the security deposit of Rs **** (Rs Two thousand five hundred.).
On **nd Nov ** i found the box is not working so I lodged a complaint wit Airtel on **nd Nov **. They have promised me that the issue will be resolved with in ** hrs. As it is not resolved the next day I started to contact Airtel but no action is taken. So on **th Nov I wrote to disconnect the service and refund the deposit. They have disconnected the service on **th and asked me to wait for * more days and will get the refund. Today, ie *rd Dec **, as I contacted them they are telling it is not possible to refund the money.