help please

i sold an engine part on ebay, then just under a week after recieveing the item the buyer then emailed to say item was badley damaged, could he have a replacement or refund, i said if he sent item back i would send replacement, i fether week pasted then item was returned, after inspection of the item, its not the item i sent out and yes this is a very damaged part, so i rung ebay and did what they adviced which was email buyer and state that it was not part i sent out and therefore wouldnt be sending a replacement or refund. Now buyer has filled in a eBay Resolutions stating that item is not as discribed in listing, he has also left me a negitive basicly saying i have muged him of his money. I do have photos of item i sent and will take photos of item recieved and send these to ebay, but im worred he has also requested my contact details so now got phone number etc. What else can i do we are talking about £150 so not small money to me. And as i suffer very badley with nerves im even scarried to anwer door or phone. any advice please, thank you in advance