Made for Summer promotion voucher nonredeemable!!

My parents signed up for a contract for a Samsung S8 through Vodacom in order to get the R4000 travel voucher as part of the Made for Summer promotion. After following the necessary steps they never received their pin in order to retrieve the voucher, Flight Center didn't answer their phones and when they finally got through they know what they were talking about, and after trying numerous times, even visiting the office in Cape Town, they were told that the voucher had expired and therefore cannot be used. How was no one able to assist them? And they were unable to use the voucher! I would've complained sooner had I known but how can trying to use a voucher so difficult, and the process stalled so that the voucher expires. Someone please needs to explain to me how this can happen and this voucher needs to be reinstated for them as they were never actually given a fair opportunity to redeem the voucher.