Cannot open commands

I was making a world based around mobs, which I'll nickname as ''World 1'', when I locked my difficulty ( normal ) for when I turned on survival mode. I then tried, without turning on survival mode yet, to make a command. I pressed the key, and the commands would not come up. I checked my controls, and saw that I pressed the correct key. I then changed the key to something I knew worked already, in case the key was broken. It wasn't, the key was correct but the commands just wouldn't come up. I then deleted World 1, to make World 2. I went to The End, tapped the key, and it would not work. I opened my notepad, and pressed the key on there, and the key worked, so it just doesn't work on the game. I then closed my game, and went here to report it.