Problem Buyer Opened a Refund Claim for Bogus Fault. How do I escalate the claim?

Hi all, I'm hoping someone can help.

I recently sold an item that was in excellent condition with no problems at all, practically like new.

A buyer with newly created account payed late as they didn't have the money at the time of the sale, then asked questions about the item after paying for it only to recieve it and then wanted to get a partial refund and negociate for a partial refund some days later for a problem that doesn't exist physically on the item. I declined this as it was our own personal item and took very good care of it, very lightly used and knew everything about it and it worked perfectly with no problems at all. The listing description was correct with many clear large photos of the item.

Straight after this they must have spat the dummy and opened a claim for a full refund. I explained to them the same thing I did when they first wanted a partial refund but have had no reply. In the opened refund claim I uploaded a full resolution photo of the problem area where the problem doesn't exist.

I might also add that they didn't have an actual persons name for the shipping address, no phone number and it was one of those pickup points.

It seems to me that I've been targeted for a type of behavior that happens now and then when sellers want to get things much cheaper after recieving it and making up any excuse to get it cheaper. Essentially blackmail. This is the first time I've had a dud buyer like this in well over 10 years. The item was packed very well and the buyer even commented on how well it was packed.

Where do I stand on this as a seller? I don't seem to have any link to escalate the claim and have the case handled by a real person and not have the automated process refund them on the refund due date.

Now if I'd made an error in the listing description, I'm more than happy to give a partial refund or full refund but this isn't the case here.

Cheers.