I have a buyer that is after a refund for some pc cables that were purchased Back in...

I have a buyer that is after a refund for some pc cables that were purchased Back in ** September ****,today ** November **** almost * months later he has asked for a full refund due to one or some of the cables being burnt and not working and also claims one plastic clip had been sliced by me to fit a corsair psu. I have offered him a patial refund as the cables were perfect when he recieved them and would have noticed well before now if it had not been working, The main discrepancy is that the cable were sold as "BitFenix Alchemy *.* PSU Cable Kit EVG-Series Supernova" which are not corsair compatible yet he has told me he had to purchase an new corsair psu because the cables did not work The cables are Not Compatible with corsair and will damage the cables if used in a psu that is not supported . I think the buyer has realised this now and just wants to blame me the seller , Can he do this and seeing as the item has been in his position for over * weeks well past the **day refund policy?