Audacity 1.2.4 has been obsolete for quite a few years and is no longer supported. The current version of Audacity is 2.0.3 and is available here: http://audacityteam.org/download/
What has happened is that you have overwritten the audio data from the project, so you have the “project” but no audio to go with it. As far as I’m aware there is no way back from that. (Audacity 2.0.3 does not let you overwrite previous projects).
I don’t understand what you did unless you go through it step by step with specifics about names of projects.
Even 1.2 should warn you if you are overwriting another project using Save Project As. Is that what you did?
Is it the project you overwrote that you are trying to get back?
If you overwrote the original then you still only have one project called that name, so I don’t understand what you deleted. Perhaps you should get that back from the trash?
Does your version of Mac have Time Machine running, so you may have a backup of the lost project saved to an external drive?
If you did not close Audacity yet and had the data you overwrote open in the same project window you may (depending on what you actually did) be able to Edit > Undo your way back to the previous data.