Airtel — Security deposit not refunding

I have taken airtel dth xstream box on 15th may 2021 and airtel has taken 1500 as a security deposit with a condition that i have to use it for atleast 1 year and after 1 year when i am disconnecting dth and asking for refund of security deposit, airtel is giving various reasons for not refunding my security.
On mail i received reply that my connection is in inactive mode from 1st june to 11th june 2021.. and when i got a connection there is a offer that first month of service is free..which means from 15th may to 14th june 2021 i got free service then how it can be possible that my dth is inactive at that time. Airtel is making fool of everyone and looting innocent peoples money.
My airtel dth connection id is +[protected] and my contact number is [protected]

Please help me to resolve issue as early as possible.
Thank you