Buyer wants to return an item that does not workdue to his operating system

[simas-stuff]

I have a buyer who bought the sims 2 plus 12 exp packs from me. he says they dont work and requests a return. After several converstions with him where i didnt know if the games had arrived broken ( i test all games before sending) it turns out he has windows 10 and they wont run on windows 10. I explained that it is up to him to ensure before buying something that it will work on his operating system. I agreed that he could return them (they are sending from Israel and i'm in the UK.) He still writes to me everyday and has now said that he is not happy with my service and has demanded a refund even though I still have not received them he also said he will leave negative feedback. Surely it is up to him to make sure what he buys will work on his system.

Am I in the wrong here? I fell threatened by his attitude and his belief that I knowingly sold him something that was defective when it is not defective.