Not all products are refundable, this is always mentioned on the product page of the product that you ordered.
Has the product code already been sent? In that case, it is unfortunately not possible to cancel your order or return it.
But for most products, you can cancel it up to 14 days after placing your order. To cancel your order, please send an e-mail to our customer service department at email@example.com. Clearly state in your e-mail which product it concerns, the order date, order number and your (contact) details.