Winter balaclava hat

I bought a Kivat winter hat for my daughter. Second size, in lilac color with a unicorn on top. The hat's head hole size is 9cm in length, 9cm in width, 9cm in diameter. I thought the hat would fit, so I threw away the price tags, unfortunately, the hat is too small, the store refused to exchange it without the price tags, I also have the receipt for the purchase. The hat is new. Last price 28 euros.