Still no feedback from Buffalo on either my email or phone call from last week.
Another call to them today had the same result, they are sticking to the line that I must just pay them, pointing to their own online Buffalo invoice as “evidence”, they won’t even acknowledge verbally whether they can produce any customs evidence.
Banggood responded via email in typical fashion, again showing no understanding of the problem at all.
I guess I am going to have to lodge a Paypal claim.

Edited to add - Paypal case is now lodged.

Banggood response below (from yesterday, before Paypal case lodged):-

Thank you for contacting us .

Regarding your order 60022464, we are sorry to see that your order was withheld by the Customs.for your request if you can pay tax from email sent by Buffaloex,we confirmed with our related colleagues that you can pay them from email you received ,for admin fee ,we kindly suggest you contact shipping companyBuffaloex whats it for first .

If you need any further information or assistance, please do not hesitate to contact us.

Best regards,

Nancyy