And you have all the documentation to prove that it is not the case. 

So you have the opportuntiy now to move on from the to and fro communication that did not appear to be getting anywhere, and carefully prepare a considered response that is clear and objective and references your supporting evidence.  Including referencing details provided in the listing description.

I suggest getting your documentation such as purchase receipt / warranty etc etc scanned and ready to upload, pdf all of the ebay messages between you and the buyer before and after sale for upload as well .... and then take it from there.