DISGUSTING SERVICE FROM TAKEALOT

I Bought a product from Takealot, it did not work so i requested a return pick up and for it to be replaced! The product that I bought had a 6 month warranty. Once they collected the item, i was informed via emial that they have checked and it is not working, however, they cannot send a replacement as the said item (which was on special at the time of purchase) is no longer available from the supplier (i checked and they still have stock of the same item) i must now re purchase this item at a higher price?? how can they offer a product with a warranty and NOT replace it if it's faulty and returned!!