Idea Cellular — demanding dues amount already surendered sim with clear all overdue amount

SIR I had three IDEA Postpaid numbers and on 13th Dec 2014 i surrender two number and intimate them by mail ([protected]@gmail.com) i am having copy for the same then customer care executive demands me my id and address proof for closing my numbers and i sent scan copy for the same. after that they called and told me for pay overdues charges Sir i again told them i had close sim i already pay all my overduebill amount which last generated and them after few months they again start calling me tried to threting me from this number [protected] and she told me that she is from consumer forum and she is having a forzery case against me. i am having a proof of my paid bill receipt Sir they are mentaly puzzling me pls help me what i can do i am having proof of mailed copy and also proof of intimation of idea care in which they confirm me for termination of my above numbers today ie. 31/07/2015 they sent me notice by lawyer NITIN SINGH BHATI for payment of Rs.921/- & Rs.882/-