How do I contact an eBay representative?

Hello community, I'm writing to tell you that I purchased the following product: Tonicol 600ml 12pk Order
06-13919-41080
Date purchased
December 2, 2025. I bought it so I could offer my American friends a taste of the incredible flavor of this soda made in my hometown of Guadalajara. Well, I had my party in January, and even though the sodas arrived VERY late, they did manage to arrive in time for my party. The problem is that when I opened and tasted them, I realized that the flavor was very different from what I'm used to and not carbonted, and in most of them (9 out of 12), the flavor was inconsistent from one bottle to another. It seems like the product is counterfeit. I contacted the seller, and so far, they haven't responded, so I'm trying to initiate a return (the seller doesn't accept returns), but the eBay website is asking me to send pictures. HOW AM I SUPPOSED TO SEND PICTURES OF THE FLAVOR OR THE LACK OF CARBONATION IN THE SODAS? So, I'm asking you all if any of you have or know how to contact an eBay agent, as I don't want to lose almost $60 that I've already paid. Thank you.