Need help with a fraud from a buyer ( returned a different item ) how to deny a refund

Hello, if someone can help I will really appreciate it

I sold a pair of Bose Quite comfort earbuds, completely sealed, brand new, the buyer after 20 days of purchase opened a return because they ”cant connect to the phone”.

I always take pictures of my packages prior shipping out, and for this one, the sealed product showing the Serial number along the order sheet.

The buyer returned the earbuds, and I found that the charging base and the earbuds, are completely different, the serial numbers are not matching with the box, in case you don’t know, the box contains the serial number for everything, the charging base, and the 2 earbuds.

I contacted the buyer, and no response, then I contacted amazon and I got this

” We have checked the order and see that buyer has raised the return request with the reason ‘ Item defective or doesn’t work’ however they have returned the different item. In this case, we suggest you to deny the refund as the original item has not been shipped back to you”

That’s a good sign, but the thing is, how do I deny the refund?

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https://preview.redd.it/nbop02mzau891.png?width=1496&format=png&auto=webp&s=80f23aa64f2ad005689186616293b5670031021d

If someone has experience with denying a refund, please tell me how to proceed, thank you very much!