No stereo sound with my Beat headphone

Recently my Beats Mixr stopped playing music in stereo and I could not find any solution on the internet. Hope someone within the Apple community can help me out. The "funny" thing is, that both sides work okay when plugging in the cable in to the Left or Right side... but not both at the same time. I already tried with the mono/stereo button in the equalizer and on different devices.

Thanks for your time in advance

Y