The playback rate you set in the program with the
"freq" command
must match the sample rate of your audio. You are correct that Audacity does not have a 12 kHz option, so using 11.025 kHz is fine.
You should update your program by changing the freq=12k command to freq=11.025k. You'll find this in the [paths] section of the program. Then recompile and retest the program.
There are other reasons why the audio might be playing fast, but try this first and see if it helps.