Airtel — airtel secure mislead me and now asking to pay me.

Address:

New Delhi, Delhi, 110085

Under airtel secure got my phone fixed. Before the phone is fixed they told me i have to pay 10% of cost of repair cost, which i have on recording. Now they are asking me to pay 10% of estimate vale, which i was conplete unaware of. And they very conveniently have set my phone value at rs 40000 (Invoice says rs. 28000).
I am willing to pay 10% of repair cost as i was told. But they are keeping my phone against my will and asking me to pay 10% of estimate value.
I enrolled under airtel secure after watching their youtube video about airtel secure, which also says 10% of repair cost.
Problem 1. They are not returning my phone even after it is fixed.