I am afraid you dug the hole you now find yourself in.
First, it is best to wait to reply to the negative feedback until you have exhausted all your removal efforts. It can take persistent effort and multiple tries to accomplish this.
Secondly, when leaving a follow-up comment, never use it to call the buyer a liar and a thief, or devolve into any name-calling. That likely sealed your fate.
The buyer specifically states that their negative feedback is not due to the fact they didn't get their item, but because of your response to them when they reached out to you.
Your follow-up comment just reinforced the validity of their complaint about your handling of the matter, and emphasizes the need to always retain one’s professionalism. Especially when faced with an unhappy buyer.
The space for the seller’s feedback response is the most valuable real estate on eBay. That’s because it can make or break a seller’s reputation—but not how one might think. The negative itself is often not as damaging as an ill-worded, ill-advised comment by the seller. That can cause the greater harm.
The audience that matters is your future buyers. Now you have just shown them how you handle a buyer who has an issue.
It costs a seller nothing to give an unhappy buyer the benefit of the doubt initially. And if the buyer is treated with respect, it will always stand a seller in good stead.
