Question: What happens if the wrong wall is pushed out and someone notices and a player picked and racked their tile?

Answer:  Below are the rules for when a player pushes out the wrong wall:

• If a player pushes out and a tile is picked from the wrong wall, the player who picked from the wrong wall has a dead hand. The other players continue until the wrong wall is exhausted and then then the game proceeds from the correct wall.
• If a player calls Mah Jongg while the wrong wall is in play, they are entitled to the win and the player who pushed out the wrong wall pays for the table. 
• If a player pushes out the wrong wall before the prior wall is completed and a player picks from the wrong wall, both players’ hands are dead.

Source:  Mah Jongg Made Easy 2024 Edition, pg. 20, #16 (a), (b), (c)