My HTC M9+ headphone jack's right channel just stopped working. What could be the cause?

[AC Question]

Yesterday night I was using my HTC One M9+ phone, and it was working normally. I was using and old headphone that had a dead right channel, but due to cut in its cable. Before this incident it was working normally on my car's AUX. When I used it today once again on my car's AUX, the right channel was not working. I tried another good headphone, but the problem remains. Could it be a software problem? Or is the hardware faulty?
Bearing in mind that I bought the phone 3 months ago.