I'm trying to demodulate an AFSK signal. My device uses 1200 baud rate and 1200/600Hz as mark/space. I tried using almost every software for demodulation, but nothing worked. Most recently, I tried QTMM AFSK1200 Decoder.
That does not sound like 1200 baud AFSK, which is probably why you can't demodulate it with your software.
Here is 1200 baud AFSK as used in amateur radio:
Note the first of these is compressed (.ogg), so probably can not be demodulated. The 2nd, however, is not compressed, so you can feed it to your software as a test.
Notice how these have a narrower frequency range. They sound vaguely vocal. The squawk at the start of each packet, which is used for synchronization, is also very distinctive. The squawk consists of an alternation between the two tones at 1200 baud.
Your sample has a much wider frequency range. It has a "windy" quality to it. There's no audibly discernible squawk at the the beginning.