Amazon India — regarding cash back - lg g6

Address:	Ahmednagar, Maharashtra, 414003
Website:	Amazon.in

I had purchased the lg g6 full vision (Astra black) mobile online from amazon india ordered on 29 april 2017 & order no.#[protected]. At that time offer was cash back of rs 7000/- if we purchased in that time & same advertisement is published in the daily news paper. Same paper cutting photo is with me, same was ordered by me in prescribed time & i got the handset & paid the amount by sbi credit card.
As per there conditions after three month i called amazon regarding my cash back offer & they told me that it will take 3-4 days more and complaint has been forwarded to concerned department, from that day i had complaint many times in last 3-4 months. I had send them e-mails also they responded me and again assured me that it will done in 48 hours. Last e-mailed was send by me on 28/10/2017 and again they given me reply that same amount will be credited in bank account with in 8-10 days.
But after 20 days of my complaint nothing has been done neither they replied me nor they credited the said amount in my account by amazon india.
Now i wish to file a case against the amazon india regarding my cash back of rs 7000/- and also harasshed me. I also want to filed case of harrashment against them.
Please look in to the matter as early as possible
Thanking you