Avongirl78 Hulme

Hi there I am hoping someone can shed some light. I am not VAT registered but sell small on Amazon they have charged me VAT through Luxemburg. I have tried to get this refunded as have many, however, they tell me I need HMRC to send me a letter to prove I am a sole trader. Now here lies the issue HMRC say they don't send these either in PDF form in email or via post. Do you know what I can do? They have withheld my payments too