Hathway broadband Indirapuram - Getting unwanted calls from Hathway from last 6 months

Hi I have taken a Hathway connection in feb**** and paid three months advance but looking at there service changed the service to other ISP in a month itself . Never asked for any refund . But these buggers are calling me continuosly after completion of * months . To renew . I am so much frustrated and don't want to use abusing words to the callers as they are doing there work . But how many callers I need to tell them that remove my number why don't they have a system that if you don't want to receive the call just remove that number . Tell me what should I do . File police complain . This harassment is making me more and more aggressive day by day and effecting my work as a person