Paytm Mobile Solutions — product cancelled after dispatch from paytm

Website:

paytmmall

I had ordered for bluetooth headset on paytm and finished my payment, there was also some offer of cashback running with i availed, order was placed successfully, money was paid via debit card and item was confirmed and shipped however the paytm cancelled the item on its own, while i try to contact customer care through difficulty they mentioned that item was out of stock, so seller had cancelled the order, a) how the item which is out of stock be dispatched, and i rechecked on the website the item was still in stock however at an higher price now, the paytm/seller felt they could cancel and cheat the customer
B) paytm owes its customers the product not just the money refunds, why to waste the valuable time of customer when you're not ready to be on the promise of item..
I am attaching the mail from the paytm with order id from paytm.
Thank you

Item shipped
On thu, 28 jun 2018
Order id - [protected]
Delivery by sat, 30 jun 2018
Track package

Sony wi-c400 neckband (Blue)
₹ 3290 ₹ 3990
Macc55 applied!
Rs1810 cashback will be added to paytm wallet in 24hrs of shipment.