Even I was facing the same issue, whenever I tried to plug in the headphones and tried to listening the music, always I was disappointed as there was no sound nor nothing, except the headphones plug in and plug out sound. I tried a lot but the problem was unresolved.
Also, gifted myself with a new headset but still no improvements, which only made me disappointed and angry, as I had bought this iPhone 7 plus just 3 months back and this is the problem I'm struggling to overcome.
It was unclear and uncertain, until I thought of giving a try and decided to take chances.
1) I connected my headphones with one of my friends handset and it was working just fine. This made me think that the headphones are all okay.
2) I tried to see if there is a problem with my Bluetooth and that the sound is getting diverted, but it wasn't. I scrolled up the control pannel tapped on the airplay mirroring which showed no device.
3) I scrolled up the control panel and under the volume you see a iphone logo , I tapped on it and selected iphone.
4) settings>sound and haptic> ringer and alerts >change with buttons option : tapped and made it ON.
5) Then at last Opened Settings > Music > Volume limit: increased the volume to MAX, returned back and turned ON the sound check.
6) Switched off the phone and turned the phone On, then connected the headphones and it started working just as it used to work before. This is how my problem got resolved. You too can try and hopefully your problem will also get resolved. Thanks.