Did you use Night Shade? Night Shade doesn't take weakness or resistance into account (but still does not effect types it is immune to), as it does damage equal to the user's Level.
If you didn't, what move did you use against what Pokémon?
The Psychic type Pokémon you could've battled are Munna, Musharma, Woobat, Swoobat, Espeon, Sigilyph, Gothita, Gothorita, Gothitelle, Solosis, Duosion, Reuniclus, Baltoy, Claydol, Elgyem, Beheeyem, Spoink, Grumpig, Lunatone, Solrock, Starmie, Bronzor, Bronzong, Beldum, Metang, and Metagross.
Only 5 on the Pokémon you could've encountered wild/in a trainer's party take Neutral Ghost damage: Bronzor, Bronzong, Beldum, Metang, and Metagross. If you fought them and used a Ghost type move, your attacks would've hit neutrally.
Source (for all the Psychic Types)
Hope I helped!