They sent me the wrong order.
I sent it back, as per their request.
Today, I got a request from them to fill in an RMA so that I could send back the elements of the order that I wanted to send back.
But I can't. A) what I received included none of what I ordered, and B) I already sent it back, via a tracked service, and it was signed for by them.
So I went on to their Live Chat again, and a nice person who went by the name "Mary" sorted it out, I think.
I don't need to do the RMA.
They'll find the stuff I actually ordered, which (I guess) is lying around somewhere in their warehouse wondering when it'll be sent, and send it to me. Failing that, they'll have new stock in the warehouse within a day or two, and send me that.
All in all, Mary says they'll send out my order within 72 hours. I have, of course, recorded the chat transcript (and I'm sure they do too).
So, with any luck, I'll have it by the end of the week. If not, I'll get onto their Live Chat again...