Airtel — not refund my deposited balance for airtel landline

Address:

Jaipur, Rajasthan, 302019

My account no [protected]. I disconnected my no and they told me refund my balance which is around 16, 000. Asked me cross cheque i sent cross cheque then they asked bank statement and said our account department required that i sent and till today no payment arrived. I chased several time and around 50 email chains i have as a evidence that they do not want to give my money back. Now it's 4 months. Could you please let me know how to proceed legal activities.