Hathway — Continuous call from customer service for the renewal though I have disconnected the account 4 months before

I was in Kelambakkam (Kanchipuram dist) for my studies and I had a hathway broadband connection (Account number - [protected]). I shifted back to my hometown since I've completed my studies. I raised a ticket to disconnect my hathway account and returned the modem 3-4 months back. But even today I get about 3-4 calls every day from the Hathway customer service asking me to renew my account. I have already told them multiple times about my situation and asked them to delete my details from their database. But it still continues and I have no idea how to cancel them. I even blocked so many of their numbers. But they keep calling from different numbers. I fear that out of frustration I might scold the customer care executive (I disconnect the call as soon as they tells me that it is from Hathway).