Trai — airtel dth unethically wants me to pay for nothing.

Dear sir/ma'am,
I got my set top changed as i was told to do by the airtel customer service representative on 2nd of january 2020, since my set top box was loosing signal and stopping to work again and again in clear weather. We paid for the engineer visit and also for the changed set top box which was an old one since their policy states that they can't give a new one. I was told that the now changed set top box has 6 months warranty, which was fine.

Now, till 2nd of february 2020, it was working fine and suddenly stopped working in the evening. I again called the customer care and they told me that they will again change the set top box, and in the same way last month, engineer will take the visiting charge and since the set top box was given 6 months warranty, they will replace it for no charge with another set top box which will have only 1 month warranty.

Now i told them that i don't want to be paying 150 rs extra every month for the engineer visit, so it would be kind if they told me where that engineer comes from, so that i can take my set top box there and get it changed myself.

At which, they said that that is not possible, i'll have to pay them every time their faulty set top box stops working.

The set top box is totally controlled by airtel dth and there is no way for us to know why it suddenly stopped showing anything, and i am unable to understand their desperation to make me pay for nothing.
I have also attached the last months receipt of engineer visit. They did't provide any separate receipt for changing the set top box, but it was marked on the same receipt.
Thanking you

Aman jain