Different seller claiming to sell my product, different packaging, how to take action?

So using the 'GTIN exemption' I sent images to Amazon of my product (Standard Thinners) with the brand logo in clear view. I was granted exemption so that in future I could list my branded products without a barcode.

For the last year another seller has been claiming to sell my product and has done very well. Whilst their product is essentially the same, the packaging label and branding isn't.

Unfortunately because the brand/product is not trademarked it seems I have no recourse to stop them or anyway to take action. Plus it seems I no longer have control over editing the listing details.

Does anyone have any experience with this kind of situation?

Any help would be greatly appreciated