Isolate tone from recording

It would appear that the tones are not 180° out of phase. If they were, they should reinforce each other rather than cancelling out.

If you zoom in on a section where there is little sound other than the tones, you may be able to see the waveform. If in doubt, post a short sample in WAV format (https://forum.audacityteam.org/t/how-to-post-an-audio-sample/29851/1)