Two different doors, depending on what you need.
Orders, payments, delivery and refunds are all handled by the retailer where you completed the purchase. Open your order history there and use the contact options on the order itself; that is the fastest route by far, and the only one that can see your order.
Wrong measurement in a product note, a broken link, a piece that has left the range, or feedback on the catalog itself:
We read everything. Corrections to product facts get priority, because the measurements on these pages are the reason the site exists.