Airtel — iphone upgrade

I purchase an iphone 7 on october 7th 2016. During the launch of this offer, i was promised by airtel that i will get an iphone upgrade every year. To abide with this offer, i had to pay 20, 000 inr downpayment and 1334 as interest for 12 months. We are not towards the end of march and my issue isn't resolved.

I was contacted by nodal officers and they have promised my phone to be upgraded to either iphone 8 or 8+, however, they are asking me to pay the emi for 12 months for the upgrade phone post which that phone would be mine.
Emi details
Iphone 8 - 5300
Iphone 8+ - 6075

This is totally ridiculous. What will happen to my present phone? I have paid 36, 006 (20, 000+16, 006) for this phone. Who would pay 36, 000 to use a phone for 12 months? I need justice for this.