Reliance keep on sending me legal notice

One years before i have brought reliance data card and it was not working properly after several months, i called customer care to fix the issue but they failed, after several week i called them and asked to terminate the connection but they not responded me properly. Even the customer care people not piking my call. one month later i have received bill for the month, I called them and requested again to terminate the connection but they asked to me to pay the bill for termination, after several conversation i told them your data card is not working also i have already requested you to terminate the connection, finally i told them I am not using your service, so i should not able to pay the bill. after few weeks they keep on sending me legal notice message to my mobile.some people called me and threaten me to pay the bill else they will gonna take legal action against me . I explained my side but they too adamant to collecting money from me, finally they reduced some amount and told me to pay. I paid it. now they asking remaining amount and again they repeating the same. Please help me for this situation.