Reliance , modem — modem disconnecting problem

I have bought a reliance hub (modem). it was working properly only for 2 months. after that it is not working properly when i connect it and click "connect" it gets connected and with in 5 seconds it automatically disconnects itself. I don't know what to do so i called a customer care and told the problem. they said go to the nearest Reliance showroom and tell the problem. So i goon to nearest Reliance showroom and told them nd there was no proper response from them. the problem was there for 3-4 months and no body from the reliance cares for it but they are correct in sending the monthly bill only it is not at all working why should i pay for in. one day from pondicherry a person from reliance came for bill collecting and i said about the problem and i don't need it you take the hub with you but he said i will send a service engg. for the problem but no one came. i called the nearest Reliance showroom and i asked them are you going to correct the problem are i have to complaint the the nearest police station.they said don't do it please if you put a complaint on us we already have some complaint on us in the police station. if you give our dealer ship will be canceled.We asked for returning the refundable deposit amount they said they cant do that they itself gave an answer you come and give the hub , for the refundable deposit amount you came purchase a reliance product for it. but they didn't do that also now i received a letter from Reliance head office to pay the bill or legal actions will be taken. now wt can i do.