Should I respond to legal notice sent by Broadband provider?

I received a legal notice from Internet service provider based in Faridabad for Non return of the equipment they installed at the time of Subscription. One of the devices got stolen from the roof and i have informed them through emails and call. my subscription was on prepaid basis for 6 month starting from 30 May 2016 to 30 nov 2016.I have dropped the email about stolen device on sep 18 2016 and had few conversions over a email about installation of new device. After that they didn't reply. They didn't communicated with me afterwards till Jan 15 by saying that if you will not return our equipment’s we will start legal proceedings. On jan 21 2017 they send a legal notice by stating that return the devices or pay 5000 rs for device and 3000 rs for not continuing the services plus 2500 legal expenses? At the time of subscription they get me signed the Subscriber application form where they have mention that all the equipment will need to retun. My question sis what to do in this condition, they didn't communicated ‘me before. I have not received any calls or emails from them from Sep 21 2016 till the day i have received legal notice. They directly send a legal notice to me.