Usually music not playing through the auxiliary port can be fixed by replacing the AUX cord. AUX cords are notorious for breaking and being unreliable, so the first thing you do should be to try using another auxiliary cord you may have around the house to see if that fixes the issue.
You should also verify that you are in the correct mode to play music through an auxiliary input.
Since you mentioned that there is a small crack in the AUX port itself, the port may need to be replaced to properly play music again.
For AUX port replacement and mode verification please see the respective help sections of the Troubleshooting Page.