Vodafone India — harassment over calls and emails for payment while there is refund for me

My name is naval kishor, user of one mobile no [protected] which i got ported from vodafone to airtel. At the time of port, i paid my vodafone bills twice, and after port i got the confirmation from vodafone customer care that i will receive the refund in the form of cheque. But on the other hand, i have been receiving many calls and emails for payment of rs. 561.00. I explained on calls and shared the proofs of payment and explained that i have no amount due rather i will receive refund.
Even after raising issue to customer care, i at last wrote to grievance department after receiving an email threatening me for legal actions. After email, i received an call and the vodafone executive, ekta, apologized and promised that i will not be receiving any calls or emails on the same. However, it is not yet stopped, i again received email on 27th aug regarding legal actions for not making payment of rs. 561.00.
This is now getting unbearable. I don't how would they stop, so now i am finally writing to consumer forum to get solution over it.