Nextra Teleservices — nextra security deposit refund

Nextra stopped giving me services in december 2017 and then in january they picked up the router and not refunded my security deposit yet. I called there customer service team several times and even wrote several emails to customer service, nodal officer, appellate, mr ankit singhal, and mr. Jagmohan singh, but still haven't got a refund. They now do not even reply.