When you import items direct from China you can't assume that there is anyone to complain to.
If the item had been damaged, it would have been covered by eBay's money back guarantee.
To complain abut the delivery you could theoretically complain to the UK courier, if you can find out who they were. But there is no guarantee that they take any notice as the contract for delivery was with the seller in China. You could complain to the seller, if you want.
Unless something is damaged, complaining about poor behaviour by couriers seems to be a lost cause. The whole industry has become like the Wild West, with "low pay by delivery" drivers desparate to get rid of their parcels. The duty to leave items in a safe place has been almost universally replaced by dumping items on the doorstep, in the garden - or even in waste bins left out for collection! Like you, I have found that explicit instructions where to leave parcels are simply ignored.
With your item being imported from China there would have been no UK statutory consumer protection anyway. Welcome to the 21st century world of high tech online shopping, and low tech delivery. Delivery issues have become one of the bggest risks of buying on eBay - where delivery is attempted but no-one is home, or items are delivered to the wrong address eBay's money back guarantee does NOT reliably protect buyers.
