Given the incorrect cellphones

On the 30th of December 2015 we bought two cellphones at sterns Eastgate Mall. Before buying the cellphones we explained to the saleperson that we need cellphones with whatsapp and then she said Nokia 220 is the best phone that she can give to us because it is affordable and it has whatsapp as well. After paying for the cellphones the salesperson only told us that we can return the cellphones within 7 days after the day of purchase if we are not happy with the cellphones. We bought the cellphones and on the 31st of December 2015 we tried to download whatsapp only to discover that the phones does not have whatsapp software. We took the cellphones to sterns and explained to Peggie that the phones that were sold to us are not the phones that we requested because they don't have whatsapp software and they are not even able to download documents or anything from the internet. Peggie told us that according to the Policy of sterns she is not allowed to take the cellphones that are returned even though its before seven days. She referred me to Vodacom for help but Vodacom said Sterns must take the phone because it doesn't have software for whatsapp. Peggie told me that she can't help me.