Airtel — No refund has been received after disconnection of Broadband account

I disconnected my broadband connection in the month of May, and requested airtel customer support team to refund the security deposit amount they take during the time of connection.
My airtel Xstream fiber ID[protected]_ap
Airtel account number- [protected]
Then they asked me to drop them an email on their official mail id [protected]@airtel.com sharing a cancelled cheque or a bank account statement. So I shared them a cancelled cheque on 18 Jul.
Post that they replied on that email that a security deposit amount of Rs.1732.21 has been already registered through NEFT.

But I never received a refund. Then I had to tweet them in twitter, where their social media team contacted me and told that there's problem with the cancelled cheque, post which I also shared them my bank statement in their DM. Still then they kept on saying we are processing your request, and it's taking longer than usual. It's now September 30th and I still haven't received a refund. Now the broadband connection stands disconnected but my money stays with them.