Phone with SAMSUNG ADH sold, not what I got...

I went to the Vodacom Eikestad Mall Branch in Stellenbosch to upgrade my wife's phone. I needed a Samsung phone with two free screen replacements (ADH) and it will be nice if the phone is water resistant. I was shown three phones, and selected the Samsung Galaxy A3 as it was similar in size to my wife's previous phone (the Blackberry Z10). The person that assisted me indicated that that phone is not water resistant. I again asked if the two free screen replacements is included - he confirmed it, stating that I must just install the ADH app and register my wife's phone. If the screen breaks I can bring it to the store or any Samsung repair center. When trying to install the app, it indicated that the app is not compatible with the phone - I searched the internet and found that the Phone's screen is not protected with any of the Samsung ADH offerings. My wife returned to the store to complain - they indicated that the phone could not be returned/swapped because it was already used. They told us to consider insurance that can cost up to R100 for the phone. Vodacom needs to take responsibility for their mistake - why do I need to pay for something I specifically required.