Just stay cool. Don't let him intimidate you into doing anything. If he's talking about fighting you, don't worry about. Just brush him off, he made the choice of buying a phone. I've found that in every hairy experience I've been in, keeping my calm has saved me. Explain to him that he should call the company himself to solve HIS problem. His problems aren't yours. My advice to you is to not let it come down to fighting, not over a phone. Good luck.