You cannot contact eBay about this.

They will not be interested in any video aside from the fact it cannot be proved it is of the same item in question.

Has the buyer opened a case for item not as described / faulty?  Then,  you will have to accept it,  as cases are all automated,  no human contact.  Accept it withing 3 days either fully refund through the case details or send a tracked label for its return.  Here you do not refund until it's back with you,  you'll have 48 hours to refund.

Stick withing those timelines,  and your seller performance will not be affected.

If you then feel the refund was unjust,  and i f eBay step in and refund, should the case be escalated, if you think the decision for the refund unfair,  you can appeal, link below shows the process.

I'll admit it's not easy,  eBay do not see the item in question and they do tend to side with a buyer's view, but worth a shot appealing.

https://www.ebay.co.uk/help/selling/managing-returns-refunds/appeal-outcome-case-seller?id=4369

@georco22