Disgusting policy preventing WhatsApp data purchase.

I have been trying to buy WhatsApp package for my mother who has an MTN contract only to find that this does not work via her MtN app.. then phoned customer service to be told the ******* "that she cannot get a Whatapp voucher as she has a contract phone and that she has to buy standard data" Huh! Which costs way more than a WhatsApp voucher data, and when using straight data, the clever phones keep using up the data on background stuff. This is honestly quite a disgusting restriction. (Not allowing a contract holder to buy WhatsApp vouchers).