As mentioned by others, Amazon owns them. I used to use them until I found out about that, then switched to https://blackwells.co.uk/ and https://wordery.com which are usually pretty close price-wise and also offer free shipping.
Amazon owns bookdepository
I don't know it, I live in Europe, not sure of this is a thing here
I've ordered from them many times to Hungary, it works well.
I work at Book Depository. We ship to almost every country in the world, and certainly to every country in Europe.