Samsung and MTN give us expired vouchers

Both my partner and I took out contracts with MTN on 23 and 24 July 2018 respectively for the new Samsung Galaxy S9 smartphones. Much to our delight we saw that each phone came with a Samsung voucher to the value of R500 "towards any qualifying Samsung Original Accessory" as indicated on the voucher. On 10/08/2018 when we were able to go to our Nearest Samsung Store to claim our vouchers I contacted the Samsung Store at Clearwater Mall only to be told that I wasn't able to claim the vouchers as the vouchers had expired and voucher claims were apparently extended until end of July 2018 . I must say that I am disappointed in the Samsung brand for providing misleading information and creating unrealistic or false expectations. Is it really right/fair/ethical that other person's who took out the exact same contracts as we did were able to claim their vouchers to get their Samsung original accessories and us not?