Why can't I use any commands or even talk in this

[mattiecraft]

I just downloaded tekkit classic and I try to use a command but the "/" key doesn't do anything, so I try to chat and the "t" key does nothing as well. I just can't work it out I looked in the options and tried the config files but I can't find anything. Finally I searched the internet about this problem and I found nothing. Can anyone help me with issue or can you just not talk or use commands in single-player tekkit?

[theprolo]

Tekkit Classic is for Minecraft 1.2.5, which was before you could use commands in singleplayer without adding in extra mods for it.