Cannot create ASINs for my own brand

This should have been so straightforward. It concerns a book I have written (so there are no ownership issues). Designers working to me produced the cover art and produced the book, the GTIN (an ISBN in this case) was produced uniquely for me by the Independent Publishing Network. As I intend to publish quite a lot of my own and other people’s material I established a brand which has a trade mark and is registered with Amazon Brand Registry.
For weeks I have been trying to list the first product but I am getting the message ‘You may not create new ASINs for this brand’. But if I can’t, who can? So what is stopping the creation of an ASIN? Multiple contacts with Seller Support get nowhere but standard replies which do not indicate that anyone has read my messages.
This is incredibly frustrating and has already derailed an intended launch of this book. The lack of transparency in the Seller Central process and the absence of any evident appeals system which directs persistent problems towards someone who can apply a rational overview is infuriating.