Goldswagon parts failier and refuse to refund

I bought a caberator base plate for golf R150 At Queens street Goldwagen for a customer of mine. I fitted the base plate customer took his car just to return 5days later with the same problem took the part of and it was eaten by the fuel. Went to take the part back only to speak to the manager witch wasn't helpful at all. He insisted that I buy a new part again in order for him to help me. Since it's for a customer that part falls onto me. I can't buy a part twice for it only to fail again since goldswagon should supply quality parts. I went to goldswagon since I don't like buying from backdoor shops so I don't need to spent more then once on a part. I went with the part and invoice but still no help