Without the requested information, I can only provide you with the following general response, which will hopefully still answer your query. First of all, I am sorry to hear about the issues you have experienced in your situation.
Your rights are entirely against the seller and you can argue that they have failed to fulfil their contractual obligations by not providing you with the item you bought.
Whilst Royal Mail are ready to compensate you, only the buyer can make a claim for it so if they are not willing to do so, you cannot make a claim. You would therefore have to pursue the seller directly for compensation.
However, I understand that they are not UK-based, which will make this rather difficult and not cost-effective. You are likely to spend a lot more pursuing this legally than you will get back.
If you paid by credit card, approach the card company who could give you extra protection under Section 75 of the Consumer Credit Act. If it was a debit card, approach the bank to see if they can do a chargeback on your behalf.