Amazon India — I'm complaining about mobile phone

Address:	Mumbai City, Maharashtra, 410209
Website:	www.amazon.in

On 27 th march I ordered a Mobile phone (Moto g Turbo 16 gb) from amazon india, its actual price on amazon is 12499. Afternoon got a call from friend who shared me the promo code and said by applying this promocode you will get a discount of 7499 and pay 4999 for the mobile. I logged in my amazon account, applied the promocode and it worked then i made the card payment and placed the order.
I have received the order confirmation email from amazon after placing the order.and around evening when i tracked the order it was automatically cancelled and the message was displayed in my account, your refund of 4999 has been initiated.
My complaint is how amazon can cancel the order automatically after confirming the order and without the concern of customer they are cancelling the orders placed