not happy with service

On saturday 01/01/2016 I went to Vodacom Chats to upgrade my phone, i was then told that i have a 7 day window that if something were wrong with the phone they would replace it for me now when i take it in because the power button is faulty they telling me that they first need to send it in to see if it is factory fault or physical damage. How can it be physical damage on the same day!?? i want this sorted out and replaced not have to wait days before i know if it will be replaced or not. Assisted by Elsie on Saturday and Chase today