False advertising

I saw your ad in the news paper advertising the Pampers Giant Packs for R199.99 each. I buy the 4+ size for my daughter, on the ad it states that is works out to R2.33 per nappy. I went to buy 2 packs this morning, I just realized now that you worked it out incorrectly, it works out to R2.84 per nappy which is definitely not a bargain anymore!!! I have both the photo of my slip as well as your adverti*****t, please advise?