Spotify muted without headset

[sunshine8998]

I recently came across a bug and it's becoming increasingly annoying. i can't play songs without a headset! I'm using an iPhone 5s iOS 9.2.1. The sound is turned ON and i have put it to 100% for the both muted and un-muted setting. the spotify volume is at about 50%. I can hear and adjust the volume just fine once i plug in a headset (KOSS in case it matters), but one i plug it out again and click on the "play button" i can't hear a thing, even though the song is playing! It progresses in length count and everything.

One strange thing is happening when i'm on the spotify app but i don't know if it's related or affects this bug (this happens when i've got my headset unplugged).  I'll put the sound on 100% -still no sound-, pull down the sound button so the phone is muted, and immediately un-mute the phone. On the quick pop-up thing that comes, the volume has changed from a full bar to just 1 "square" (equalling from 100% sound to like 5%?) once i touch the + volume button it jumps up to 100% again, but i still can't hear anything without a headset. Are anyone able to think of solutions to this? i'm all out of ideas 😕