Dosmas

I accidentally traded my haunter to someone so they could trade it back and then it got stuck in her pc because she cant access pokemon from other regions. Can someone please help me get my pokemon back? I am on the gold server. My username is DosMas my trade partner is Halesyeah. I was trying to evolve haunter to get it right back as Gengar. Please let me know if you are able to help. I need that pokemon to get to the next region.

I accidentally trade my haunter to someone so they could trade it back and then it got stuck in his pc because he cant access pokemon from other regions. Can someone please help me get my pokemon back?