Discount codes do not work- False advertising

I want to buy UNISA textbooks from [URL Removed] <br> <br> I saw two promotional codes online that stated I could receive discount off of my purchase should I input the keywords UNISA and studentdiscount. This is being advertised from the Takealot website, so I assumed that it would work. I was then informed that I, for some reason, do not qualify for the discounts? Why is this? <br> <br> I have been a loyal customer of [URL Removed] for a long time, and would like to continue to be.<br> <br> Thank you