Samsung + MTN R500 voucher

I recently upgraded my contract at MTN (03/07/2018) to the Samsung S9+.It came with a R500 accessory voucher but when I try to claim it at MTN they say its only for a cover when in their advertising it says I can use it for the wireless charger as well.when I tried to check at the Gateway branch they tell me to check at the Samsung store in order to redeem the voucher.im tired of being given the run around when I just want to claim the voucher and not on a cover.Please tell me whats the way forward as there are other shops that sell Samsung accessories not just MTN and the Samsung store.