Threatening calls from Tikona

I was using Tikona broadband in Bangalore almost an year ago and disconnected the service since we were vacating that house. I have made multiple calls to customer care asking them to disconnect the service.
Now, after almost an year, I’ m getting calls from few people who claim themselves as lawyers of Delhi HC and threatening me to pay 2k as my due else a legal notice would be sent to me.
I don’t understand why I should pay for the service which I haven’t used. I have paid the bill till the last usage.
I went through many posts related to this and understood that I m not the only victim. Now my only concern is that will I be sent a legal notice? If yes, how should I proceed? Can anyone confirm on this?

Thanks in advance,
Sharmila M