Get100 when you spend R500 or more, or so they say...?

Get R100 on check out when spending R500. Advert still appears, but isn't honoured. Reply on my previous complaints did unfortunately not solve the problem. I was offered free delivery next time, thank you, but it still does not satisfy my ‘curiosity’ on the too good to be true-offer. Can however as in the past recommend the delivery of goods. Only complaning about 'voucher' that registers as NOT VALID. Curious customer