two fridges bought on same day. one door has rusted and the other not.

We bought two fridges on 03/12/2018. One fridge door has rusted terribly, and the other is perfect. They have stood next to each other since the day they were delivered. They have been cleaned in exactly the same manner, with the same cleaning products, and the one door looks terrible and the other is perfect. Aziza from Bosch simply says "we don't cover rust, and buy a new door" but this is clearly a product fault. how can one product rust and the other not. Aziza and Beecum have not bothered to reply to my last email