Hi,
Just some info for people of the procedure we when through to list a new product.
So the Amazon selling account, Amazon Brand Registry for our brand name and UK trademark are all in the company name. Brand registry is linked to our selling account.

We use GS1 barcodes for all products, also GS1 barcodes account is registered to the company.
When trying to list a new product and when entering our brand name we got an error message telling us we were trying to list a product using UPSs, EANs, ISBNs, ASINs or JAN codes that do not match the product we are trying to list but we should contact Seller Support if we think this isn’t correct.
Contacted seller support about the problem and got this reply:

"If you are the owner of the brand you are selling, please provide:

1. A copy of the certificate issued to you by GS1 showing your legal entity and associated GTIN prefix(s).
2. Proof that the legal entity on this certificate is related to your brand such as a trademark registration or website which displays your products or brand and its relationship with the UPC/EAN owner. (We only consider official website owned by the brand, manufacturer or the UPC/EAN owner - the affiliation should be clearly called out).

If you are not the owner of the brand, please provide:

A copy of a letter or legal agreement from the manufacturer, or brand stating that the GTIN you are using to list this product is valid and owned by them OR that you are allowed to use your own GTIN to sell unique products with their brand. If you are using your own GTIN, the letter should establish that there is a relationship between the legal entity associated with your prefix and the brand. The email or letter must also include the point of contact at the brand or manufacturer that Amazon can contact to verify, this can be found in the footer of the email or indicated in the text.

In order to address your concern, we will need some additional information. Please respond to this message to provide the details requested below. Please understand we do not want to provide unwanted information or any unwanted action on our valued sellers account which may lead to any inconvenience to you."

Being the brand owner we sent them the GS1 certificate, UK IPO trademark certificateand Certificate of Corporation from Companies House.
24 hours later seller support replied with " the UPC/EANs have now been affiliated with the Brand" so it was sorted pretty quickly and we can list again.
Never had any issues listing on our brand before now, looks like Amazon are checking into the type / authenticity of barcodes more now?