eBay/Post Office skanked me; do I have recourse?

Due to the number of counterfeit trainers in the world, eBay now have a system where you no longer send direct to the buyer, you send to an intermediate that verifies first then they post to the buyer.

I sent a pair of trainers that I sold via the post office to said eBay verification location.
Eventually I get messages from eBay and the buyer asking where the footwear is.
I find out from the Post Office that they tried to deliver (once @ ~8.15am) and according to their system the item was refused, they're trying to find the item and to come back and try again.

When I questioned eBay about the refusal to sign, they said, they'd never do that and that the item was posted outside of business hours, hence no one signing for it.

After a few weeks it became clear that the Post Office have lost the item.

The things that pissed me off about this whole affair:

1. Why have the Post Office only attempted delivery once? Surely you'd at least leave a card? Or try again the following day??
   
2. eBay said nothing about about ensuring delivery was within business hours. Why am I penalised for this?
   
3. Who is lying, did someone actually "refuse" the item or was there just nobody present?
   
4. Turns out I cannot get the full value of the item as it wasn't posted at full value...because when I posted, my local PO didn't ask me the value, and I forgot to ensure the correct value.
   
   

I can only claim £50 for something that I sold for £115.00

Is there anything I can do to get more money back or just cut my losses?