eBay buyer has broken laptop and is asking for refund - any advice?

I sold a laptop last week in absolutely pristine condition - no issues, marks or scratches. It was very securely packaged, and sent via Royal Mail special delivery. It arrived with the buyer on Monday.

On Thursday evening I get a return request because there is significant damage - it's clearly been dropped as there is a huge dent and broken all around the corner. It's basically now ready to be binned.

What are my options? I don't accept returns but eBay are forcing me to accept. I would have been fine to take it back if they just didn't want it but now I'm going to be out of pocket and also have a wrecked laptop.

I have a photo of the box as proof of delivery and it does not look damaged.

If they received it on Monday, how come it's taken til Thursday to apparently say that it must have been damaged before I sent it?

Any idea what options I have? I know eBay always side with a buyer but this is just blatant fraud.