Proof of Affiliation between brand and Barcode Owner?

I was creating a listing of Brand N with my own UPC which I directly bought from GS1, but keep receiving error 8572. The Brand N was enrolled in Amazon Registry by another seller and I have been approved by them to use Brand N to list new products. Amazon asks me to provide Proof of Affiliation between brand N and Barcode Owner. I have tried the following ways:

1. Asked the trademark owner to write a letter stating that they authorize us to use our own UPC. - case ID 13990693911

2. Asked the seller to write a letter stating that they authorize us to use our own UPC - case ID 14040467541

Both received the same reply from Amazon:

"Proof of Affiliation is invalid since it shows no affiliation between the Brand and the GTIN Owner. Kindly provide a valid Proof of Affiliation between the Brand N & Barcode Owner “x Inc.”.

@Sandy_Amazon Would you please take a look at my cases? Who is the brand owner Amazon is asking for? What exactly document Amazon want?