Hi, Rusty!
I am sorry that it has taken me so long to get back to you.
I have been all this while sorting out the situation with the book seller - Paper Cavalier UK (I shall name and shame!)
It proved impossible for me to contact them, as the email from them did not accept replies!
So I have taken your good advice and got in touch with Amazon itself.
It took some time to find a contact number for Amazon UK Customer Services, but once I had found it and rung it........all went smoothly.
I explained the circumstances to a very nice young man, who was extremely helpful,
He agreed that we shouldn't be put to all that palaver, when the fault lay with the seller, and he emailed the selling company telling them just that!
He has told them either to replace the book with the correct volume, or else provide us with the means to return it.
So I am now awaiting hearing from Paper Cavalier..........
Thank you again for all your help!