Swiggy — Non delivery of additional pizza

Dear sir,
While ordering pizza, it was mentioned on top of the menu as 'buy one get one' offer.When the pizza was delivered, i recd only one pizza.I complained to swiggy via the chat option & nearly spend more than an hour with three excequtives ( being forwarded to one another), without any resolution.
As per the excequtive, you could have got additional pizza if you had ordered two pizzas !!
Which does not make sense as it was mentioned as buy 1 get 1 offer.
Kindly look into this cheap gimmicks of swiggy & make them accountable for there actions