Chamet Diamond Seller Didn't Refund And Exchange

I had been doing business by exchanging my Chamet dollars and recently stopped working with one Dimone seller because of personal issues. After that, I connected with a new Dimone seller on Chamet with the name “DiamondsStar⭐💎✅” and Chamet seller ID 166880*** and clearly told him about my Chamet dollar balance. He agreed to do the exchange, and I sent him the Chamet dollars as requested. After receiving my Chamet dollars, this new seller suddenly brought up his friend’s name, who is the previous seller I used to work with, and started saying that I had to make some “back payment” to his friend. He then clearly told me that I would not get any refund or exchange unless I paid this amount related to his friend, even though my business and payments were only with him, not with his friend. I am complaining because I paid and sent my Chamet dollars to this new seller in good faith, and he is now refusing both to complete the exchange and to refund me, using an issue with his friend as an excuse. I am doing business with him directly and I am not responsible for whatever personal or business issues there may be between him and his friend. I request a full refund of the Chamet dollars I have already sent or, alternatively, that the agreed exchange be completed immediately. In addition, I ask that action be taken against this seller for this behavior so that similar situations do not happen to other customers. I also have chat and transaction screenshots showing the payment and the seller’s refusal, which I can provide if needed.