Up to a certain point, you can cancel your order directly in your customer account under Orders. 

You can also use this direct link to view your order: https://www.addnature.co.uk/query-order.html

The link works also if you placed the order as a guest.

If this is no longer possible, you can refuse to accept the shipment. After receipt of the return, the amount will be refunded if it has already been paid.