sharp boombox

[vintage50]

Hello, what should I do in this situation?

Left negative feedback saying I sold him a broken item, which was not true. Also sent me aggressive messages on WhatsApp. Before sending the product, I shoot a video review, which proves that the boombox works 100%. I have sold many boomboxes and have never sent a buyer a defective item, so as an eBay seller I have nothing but positive feedback.
The buyer carelessly damaged the boombox and now wants to beautify the product.

[ebooksdiva]

Even though you videoed the boombox as working when you shipped, you have no idea what happens while in transit to the buyer. 
Unless the buyer opens a not as described return I wouldn’t respond especially if they aren’t contacting through eBay.