Products shrink and they will not refund. Terrible customer service.

I bought a duvet cover from them and it shrunk on first wash. It was washed on a warm wash and a cool tumble. I reached out and they told me that it was not possible as they preshrink their products. Regardless of that, it did in fact shrink substantially. I do not think that they are lying about preshrinking their products, however everyone knows that sometimes steps are missed in production resulting in rejects or malfunctions. I asked them to swop it or to refund it. They claimed to run their own wash experiment and concluded that there is no shrinkage in the product. So not only did my duvet shrink by nearly 30cm, they insinuated that I was not telling the truth. It would be very easy to verify what I am saying simply by measuring. After that they stopped responding to my mail.