Ebay are very unlikely to side with you if you open a case for them to review, as the seller can prove they have posted the item with attempted delivery plus Royal mails photo all logged on their system including the map. The sellers obligation in ebays view is therefore completed. The seller doesn't have to refund, chase Royal mail nor contact you and has likely black listed you, although may still receive your messages depending on their selling preferences.
It's worth checking with any neighbours if you have any, as Royal mail are funny with safe place deliveries. They often don't take photos either when it's a safe place delivery.
If you want your money back, you're best off contacting your bank. The dispute will result in ebay taking the hit as the seller will be protected through proof of attempted delivery - what Royal mail do with their/your item is out of the sellers control.
The process will take a while, as the seller is allowed to challenge your dispute, but your bank will likely side with you regardless of what they state. It's irrelevant to the seller regardless as they will be covered by ebays seller protection policy.