Airtel — complaint on malicious calls from airtel mobile number

I used to have a number "[protected]" on my name a year back. I have ported that number out of airtel to vodafone and later i disconnected that number 6 months back.
Now am getting calls from that number to all my contacts. There's a female voice on the other end and she's calling all my relatives and disturbing them. I need to get some immediate actions taken for that phone number as the owner is using my personal details to contact people.