Amazon India - Promotion for Online Shopping not received as promised

In October ****, Amazon had launched a special promotional offer on pre-order of One Plus *T mobile phone. As per the offer, whoever pre-books the mobile by purchasing One Plus *T gift card worth Rs. ****/- before **th October would get a cashback of Rs. ***/- credited to their Amazon pay account by *th November **** and the code to purchase the “OnePlus Type-C Bullets Earphones” for free will be sent to email by **th November ****. The customer would have to purchase the phone on *st, *nd or *rd Nov to avail the offer.
I asked my friend to purchase the gift card for the pre-booking from her Amazon account and send it to me as gift. Order ID of One Plus *T gift card - ***-*******-*******. I have attached image of the Gift card I received over email when my friend booked it. After this, I purchased the phone on *nd November **** using this gift card amount from my account as I had the gift card. Order ID of One Plus *T phone purchase - ***-*******-*******.
As per the promotional offer, I should have received the Rs. ***/- by *th November **** but did not receive it. So, I contacted Amazon Customer service over Chat on *th November **** for enquiry. After explaining my problem, the Customer service representative Deepak told me that I will not receive offers as the Gift Card and the phone were purchased using * different accounts and not one. Immediately after this, the chat got disconnected before any further discussion and I got automatically connected to a new representative Moulya. I had to explain my issue again to him on which he told me that there was some mistake on part of Amazon and he would raise an escalation with the respective team. Moulya also told me that my problem would be resolved within * business days. I was happy that I would be getting the promotional offers promised by Amazon and my issue will be solved. He also sent me an email confirming this.
I waited till **th November but did not get any response from Amazon. I did not receive the code to purchase the “OnePlus Type-C Bullets Earphones” either. I contacted them again explained the issue. Pritesh was the name of the representative who was chatting with me this time. He assured me that the team is working on my query and **th was the last business day. He told me that I should wait for that day; they will send me a mail as soon as the offer is applied and my code for earphones is activated. Again there was no update from Amazon.
I contacted Amazon Customer service again via Chat on **th November. I talked to Bhim and his supervisor Amit this time. I was shocked to hear both of them telling me the reason that I will not get the promotional offer since the Gift card and Phone were purchased from * different accounts. Amit kept telling me that it was mentioned in the FAQ section of the promotional offer. I asked him for a proof of the offer with the condition mentioned as a screenshot, but he said he does not have it. He said he can send me the details only on mail but not in the same format as it was displayed on the Amazon.in website when I purchased the Gift Card. He also told me that the previous representatives had misguided me.
The Amazon.in website and the Customer service representatives misguided me due to which I had a loss of Rs. ***/- cash back and original One Plus Bullet Earphones worth Rs.****/-.
I have objections / concerns regarding the following points related to Amazon India.
*) If the condition of buying the gift card and the phone from the same account was so important and mandatory, the website should have clearly mentioned it at the top or at a position on the offer page where it is visible to the customers. What is the proof that the details they provide me now over email are correct? When asked for the exact offer screenshot, they were not able to provide me with that.
*) If both had to be purchased with the same account, the Amazon website should have prevented my friend from sending the gift card to me. On purchase of the specific One Plus *T gift card, it should have been automatically added to by friend’s Amazon account as that was the pre-condition. They should not all the customers to send such gift cards to others.
*) The Customer service representatives are either not adequately informed about the offers or they purposely kept misguiding me till the phone return date had crossed which was **th November. They kept telling me that it was a mistake on their side and will be resolved in * business days. They provided me wrong information for ** days and resulted in considerable loss and a lot of mental stress.
I have wasted a lot of time in following up with Amazon on this issue and have not got a solution. There may be so many customers like me who would have been cheated like this and for bigger amounts. I would request for a compensation for the loss I have had due to the Amazon website issue and incompetent representatives.