Refusing to exchange

I have sent my younger brother to go buy a Hisense cellphone at Ackermans’s Soshanguve Plaza and he mistakenly bought Nokia, I called customer care where I spoke to an agent by name of Nolitha she assured me that the phone will be exchanged as long as it’s not damaged. I then headed the store where they refused to exchange for me stating that I cannot exchange. I called back the customer care and agent refused to help saying it’s store decision, which puzzled me because customer care supposed to assist when the store cannot