If you are unhappy with your purchase, you can open a Dispute in the Resolution Centre at the bottom of this page.
The first suggestion is to Contact the Seller.
He may be able to offer a simple fix or tell you what you are doing wrong.
Or he may tell you to return the phone for a refund.
Be polite. This is a discussion not a fight.
If he refuses to help, ask eBay to step in and escalate to a Claim.
You will have to return the thing (I'm not clear on what it is supposed to do) with Confirmation of Delivery.
If he is overseas this will be expensive -- over $40 probably.
When the thingie show delivered (not shipped,delivered) you will be refunded.