That was not smart to order something from out of the country without first understanding the delivered cost. There is a minimum threshold amount I think, but in general you pay VAT to import from out of the EU, and if UK completes BREXIT, you will owe duties and taxes for many European purchases.
It may be possible to have the package returned to sender by contacting the local postal service, but it is an annoyance to the postal service, customs, and Forever 21. You will have a long wait for a refund, and shipping will not be refunded.
You are better off learning a lesson, paying the taxes due, and learn about duties and taxes in international ordering before you try to buy anything again from out of your country.
You probably have a fee, plus VAT to be paying as normal for imported items.