The payment was made to a neteller account, I don’t think that counts as the company but could be wrong.
As far as I know, Neteller does not let register accounts under companies’ names. At least, I have tried and was refused to do so. So it must have been just a private deal between two people. I also assume, there has been no written contract between the parties. It was just a sale of SOME assets (whatever- company’s, or personal, does not matter). The assets that you purchased did not carry any liabilities, the affiliate account did. The affiliate account’s owner has been carrying the liability of the double payment, not you. He prefered not to sell the account to you, thus he stayed with the account and all account’s assets and liabilities. As an affiliate account owner you can change the names of the web sites associated with your accounts at your will (even daily!) by just typing new names into the “personal details” folder. I am not a lawyer, but from my point of view it is the affiliate account owner’s problem, not yours.