While I was shopping, I saw that, starting from a certain amount, shipping costs are free. I reached that amount, but I was still charged the shipping costs. Why?

This can happen if you have ordered products from more than one of our partners. Each of them has its own shipping rates and its own rules on promotions. If a seller offers a promotion on shipping costs, it will only be for that seller's products. You must therefore reach the specified amount with that particular seller in order to benefit from the promotion.