Unfair treatment on faulty item

Purchased a Hisense 28L 4-in-1 Airfry Toaster Oven. Found out the item was faulty and returned it. I requested it to be replaced. They responded by giving me credit and saying it is out of stock, but it is still available at a higher price. When I queried it they said it was a system fault and will be removed of the site and is not available for purchase. And yet the item is still available, at the higher price and can be bought. I believe they just do not want to incur the extra costs of an item that I rightfully bought and am owed at the price specified. This is not fair treatment.