FALSE ADVERTISING

I saw a dress on instagram so i decided to buy the dress for my 5 months old daughter as a Christmas present, when i went to buy it at Pavillion mall they told me that it does not include a head band, they only give a head band when you have bought for a new born, but they did not state that on their instagram page, i ended up buying a dress without the had band i am so disappointed and when i tried to enquirer with the sales rep she told me that the dress is a reject they need to return it to the shop , the shop manager told me that the head band is given to new born babies only. why are they giving false advertising.