Staff don't know how to redeem promotion

I went to the Samsung Store in the waterfront in order to purchase a cover with the promotional R500 voucher from purchasing a S10. However when asking to redeem my voucher I was told that only one person in the store could redeem the voucher and they weren't there. How is that possible? That a Samsung promotion can't be redeemed at a Samsung store? Because the staff don't know how to handle it?