I got scammed selling a Hellfire in rocket league xbox

So I put up my Hellfire for £45 at first because I was unaware of prices then someone messaged me on the offer, saying that they would do it for 20. I said okay and he sent one of those fake messages saying the item was bought luckily I was told by the community that it was a scam (I was unaware because I was/am new too gameflip) . I was about to close the offer then he bought the Hellfire this time legitimately and gameflip told me to deliver it to him through private massaging he told me to deliver it to the account TheMadTrader, anyway I did i gave him the Hellfire then he started calling me a scammer (I have video proof of all of this including me giving the item) and he put the sale on hold and told me that I delivered it to the wrong account even though I delivered it to the one he requested and then he kept on making multiple excuses like I bet it’s your friends account and I changed my name and then someone else took it. This has been going on for 4 days and I want back my Hellfire or the 18 pounds ( 20 - tax).
If u was unclear at any point I can provide further evidence or explain. I have emailed gameflip multiple times tweeted at them and I haven’t gotten a response my order is

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Not such a good first time experience

Hi, I am sorry this happened to you. What is your Gameflip invite code? This can be found on your user profile. This will allow Gameflip to find and locate your account/support ticket to provide assistance.

I’m not if this is what you were looking for 45BVE1

Hey if you haven’t done so already please contact our support team at support@gameflip.com and then send us.the clip so we can continue to help you further.