S9 Accessory Voucher disappointment

I got a new contract with MTN when they had the pre-order offer with the Samsung S9, where you got the R500 original Samsung accessory voucher. The new Samsung S9 includes a cover as well. I decided then to rather use my voucher of R500 for another charger. MTN stores don' t stock Samsung original charger they only stock covers. So I went to Samsung Eastgate and they did not have stock either but said they will be getting stock in the week. So before driving all the way out there a week later I phoned them to find out if they have stock of the chargers. They did confirm that they have stock. I then explained that I want to use the voucher, when they informed me that Samsung Stores also don't except the voucher anymore. You need to use your voucher at the Mobile store. Don' t see why I must now spend like R800 for a cover because that is all you can get at the mobile stores. I just think it is pathetic that they can just change the rules regarding the vouchers just like that. So I will be losing out on the voucher and that was one of the reasons I decided to get a new contract phone again. And best part is the voucher expire end of May so I am definitely going to loose out on the voucher. I really do not need a cover. I just want a extra charger.