Flipkart — Cancellation of my orders without giving genuine reason

I ordered mobile phone twice with old mobile exchange offer and both times the order was cancelled without any genuine reason. For the 1st order, they gave the reason that order was cancelled by the seller. Second time, the reason given to me that delivery partner to deliver on my location dur to pin and address mismatch. Then, I contacted the delivery partner immediately and they gave me different reason. They told flipkart doesn't accept old phones now. The more interesting thing was an offer placed without the offer was delivered to my address. So, now I want to know the genuine reason for the cancellation of the first two orders.