exchange hustle

on the 28th October I Purchased some Items at Ackermans Church Square Pretoria but when I Got home some Items couldn't fit my son so I went back to the store for an exchange, when I got to the store the Cashier said she wants the card that I used, I told her that I scanned with My phone the I showed her the Physical card, then she said the number on the Receipt and the Number on my card is not the same, so she called her supervisor the the supervisor says she can continue with the exchange, while they checked the Items they told me that I have to bring all the Items that I bought because there was a promotion on those Items and I told them that the Ones that I did not bring fits him and they said their problem is that they have to give me a refund and they ended up doing a voucher and not informing me, what Am I gonna use the voucher for, I don;t want anything at ackermans anymore.