Hathway Cable & Datacom — hathway sent me a false legal notice for the internet which was not used after deactivation

Address:	Hyderabad, Andhra Pradesh, 500007
Website:	www.hathway.com/Broadband

I had a hathway connection about three years back. I have disonnected the connection in may 2015 sending a mail and also the executive collected back the modem after the deactivation. Now after three years i got a text message from them saying that legal notice has been sent to me asking to pay rs 3898 to clear this. What the hell is that someone charging money after the internet connection is deactivated and the executive taking back the modem and now sending a false legal notice after 3 years without any communication prior in these 3 years. How can you charge for something that the customer did not use for?