Good Products and Efficient Delivery, but Very Poor Aftersales Service

I purchased products from Hi-Fi Corporation online about 2 months ago. They carry a 25 year warranty, and I had to register it for this purpose. Firstly, the details on the invoice had several errors, but furthermore, I needed more information for registering the warranty (e.g. on the dropdown menu I have to select the shop from which it had been purchased, but the online shop is not there, and they require a serial number, which the products don't have, so I cannot complete the registration). I wrote to them, and only after the 3rd e-mail, the invoice details were corrected. But my other questions were just ignored. Repeatedly (about 4 x over the next few weeks) I tried to contact them, both via e-mail and their online platform, with no results. So two months down the line, and I still cannot register the products.