StockX complaint: Lost Item Never received Item

I have ordered an item from Stock X, it claims to have arrived however I have to received the item, Stock x has been extremely negligent and has ignored my emails for days and reply every so often, I sometimes have to email them 3 times before they reply, they refuse to do anything about my situation and has instructed me, the victim in the issue to do all the hard work and file reports to the police and UPS while they have done nothing about the on going situation. I have had to file a police report – which was no use as they said Stock x has needed to launch an investigation with their courier – which they have not. Therefore, I have taken in into my own hands to open a claim with the courier. Stock x is failing to take any action and has not reassured me at all during the issue. I am extremely disappointed with the service and furious as I feel like I am being robbed.