You don't need to contact an eBay agent. I can't believe that as a business seller on eBay for nine years you have apparently never even looked at eBay's money back guarantee?? There is a link to it in every listing, or see: https://pages.ebay.co.uk/ebay-money-back-guarantee/
All you have to do is to open an item not received case. eBay will require the seller to provide tracking proof of delivery. If the tracking record conirms that it was delivered to another address your refund should be assured.
If it had been tracked as delivered you your address, but actually delivered to another one, that would have been avery different story! You really should make yourself familiar with how eBay decides claims of non-delivery. These do not always end well for the buyer, to the point where delivery issues have become one of the biggest risks of buying on eBay.
