Amazon India - Amazon didn't send product and wasted time

So, I have been refused to get the code for the Free bullet earphones with OnePlus *t. I will take you ahead with this. It's not about the earphones, it's about the time I've put in through this process to get it right.

*. I came across the OnePlus *T prebook gift card offer.
*. I called up an amazon Official to confirm whether I can use this gift card, despite the fact that I want to eventually buy the phone on EMI. He told me to go ahead on the **th of October, and hence
*. I prebooked the OnePlus *T (Email Gift card, sent to me by my mother). Emphasis on the gift, because you can share it on email. That's what gift cards are, to begin with, if I'm not wrong.
*. I added the gift card to my account, since it mentioned, I can use it against the amazon pay balance.
*. The phone went live on the *st of November
*. I called up Amazon official, to confirm, whether this gift card will be applicable. I asked the process. The person stayed on the phone while I ordered the OnePlus *T
*. I tried adding the code, and it said "This code is already a part of this order" or something of that sort. I asked the official, if this is okay. And they said, yes. Go ahead with the order. You'd receive a code for the earphones by **th November and the *** rupee cashback by the end of the month.
I placed the order while confirming everything is right, and received the phone on *st November itself.
*. **th November I got in touch with Amazon for the code. They said, some issue has been going on from OnePlus's side, and they will send the code to the people. So don't worry. You'd get it. Wait for a day or two.
*. **th November I called up Amazon. They asked me to send an email to cs-reply@amazon.in. I did. I never received anything but an automated reply.
**. **th-**th November, got in touch with Amazon. He said that this is an issue. He will help me. He tried to give me a code, but it didn't work. And, he put me on hold to talk to his team and superiors multiple times, only to tell me that he has escalated the issue and I will definitely get a reply in ** days. I didn't get a reply in ** days.
**. Today (*th December), ** days after prebooking the oneplus *t with the gift card, I was told after calling Amazon, that my first step was wrong. After ** days, after calling amazon BEFORE every order I place, after confirming any queries I have before placing the order, and many hours of to and fro, and being told that I will get the code, and being sent a code later, I am told, that whatever I have been wasting my time at is my fault.

Moral of the story: Even if I follow everything, or question Amazon officials to make sure I don't make a mistake and do everything according to Amazon, and being repeatedly told that I will get it soon - suddenly, It's my fault. And amazon can't help me. What kind of a ridiculous service is this? How is this my fault? And why do I have to face the repercussions?

I was told that you had to buy the gift card from the same account, because you can't treat it like a gift card. So even if I added it to my amazon account, and it mentioned the gift code has already been added, I am not eligible for this.