CNA
Gift voucher not allowed

I received a R50 off R200 spent at CNA. I went to the camera section and wanted to buy an SD card for a camera.
At the till I was refused to use the voucher, I asked why, she said it's cellular.
I said this SD card cannot fit in any cellphone and it's not from the cellular section.
She replied that Scandisk is not a CNA product, therefore I cannot use the voucher.
I said no where in the terms does it say it cannot be used on camera or computer equipment and accessories.
She just repeated that I can't use it on cellular.