Firstly, you don’t need to trade with other people for haunter to evolve in this game (for future reference). There is a certain feature called the Witchdoctor that evolves mons that require to be evolved by trade for you. This is within the Black Market, before the 2nd gym, within Helios City.
The Witchdoctor resides in the eastern-most house in the Black Market. This character creates special powders which allow the player to evolve Pokémon that would normally evolve through trade, assuming that all of their trading conditions have been met." (Pokémon wiki) https://wiki.p-insurgence.com/Black_Market
As for GTS, do not use as you have seen now. It will eat your mons. I would gladly help you get a lvl 25 haunter.