I'm not sure if there's a reporting format because I don't see one so I'll just provide all the details I can.   
Time: 1940-1945 
Date: 03 FEB 19 
Location: Goldenrod City Pokemon Center 
IGN: Same as forums 
Server: Gold 
Pokemon Affected: Whismur, level 81, Soundproof ability, Moves: Fire Blast, Ice Beam, Hyper Voice, Astonish   
I tried to release a level 26 Ariados I had in my team and the game gave me a popup asking if I wanted to release my lv 81 Whismur I had in box 5 of my PC. I clicked cancel because I didn't want to release my Whismur, but it was taken away anyway and is no longer in my box. The Ariados was still in my team at the time. Is there a way I can get my Whismur back?