Unable to list any items

I am an individual private seller, not a business, and have been selling a few books on Amazon for the past few years. I have not had any issues until recently.

I received an email from Amazon saying that it was reviewing my account and asking me to upload documentation. It looked like phishing so I checked with Amazon and they said it was genuine but that my account was fine and I could ignore the emails. However the emails continued to arrive and the last one said that if I didn't supply the information within 7 days I would be unable to sell, so I contacted them again and this time they said that I should complete the documentation. I clicked through and it was asking me to verify that I was not connected with a politically sensitive individual. I am not, so I verified this.

However since then I have been unable to list any books. i keep being asked to apply for approval to sell, where I am asked to provide documentation such as manufacturer's invoices which as a private seller I cannot provide.

Customer services have been no help. They just give copy paste replies that advise that certain categories are restricted from sale because of the subject matter (I have tried a range of books on different subjects, none spurious!) or that it is to protect their customers from safety issues, which I don't understand. They insist there is nothing wrong with my account, but I can't list anything and I can't seem to get a resolution.