Vodafone India — Vodafone asking money after my number is ported

I have a ported number from vodafone [protected] to airtel, when i ported the number from vodafone, they told me the dues are cleared and my number was ported, now after some months they are sending me an email that i still have some amount to pay and i need to pay else they are threatening that they will disconnect my services and take actions. Please take the correct legal actions against the vodafone for the harrasment they are causing..