Incomplete order and unjust customer treatment

I bought a 3 in 1 stroller for my pregnant sister during the black Friday sale and didn't open the package because I believed they would deliver exactly what I ordered and paid. To my disappointment when I open the gift this past weekend it's not the order as advertised on the app. I received a 2 in 1 instead of a 3 in 1. And when I raised the issue with them they tell me about some return policy. This situation is an exception and a mistake on their side therefore should not be handled with their blanket approach. It's not like I Want to return the item all I want is the missing part of the baby 3 in 1 stroller.