The 3.5mm stereo jack has separate connectors to receive the Tip (left channel), Ring (right channel), and Sleeve (ground) of your stereo headphone plug. It would appear based on your description that the ground is no longer making contact with the first connector. It is possible that you have broken one or more connectors from the circuit board. It is also possible that a piece of debris became lodged in there or the contact has become bent or highly oxidized and is preventing proper contact.
Make sure you are using a TRS stereo jack and not a TRRS stereo jack with microphone which can cause problems.
A few things you could try before returning for repair:
1. See if you can get a single channel (L) to the headphones by pulling the plug partly out and rotating it gently. If the tip and sleeve are making contact properly, then you should get a signal to the left headphone channel.
2. Try blowing out the jack with an air can. (Look in there with an LED flashlight)
3. Take a pair of headphones or earbuds that you don't care about and LIGHTLY shank the plug a little with a pair of pliers so the the plug has a SLIGHT curve to it. The may curve the plug enough to make proper contact especially if it is rotated around a bit while trying it out.