Why wont my music stop?

I set my timer for 15-20, and i set it to "stop playing" so that the music will stop. Its stops,for a second but then it continues to play. Its really annoying cause i wake up with music still playing. Why wont my music stop? How can i fix this problem. Its really annoying, its been happening for a while.

Im case you're wondering, no i haven't drop it in water. It hasn't been damaged in any way. Its had its falls and i've spilt liquid on i but it never went inside the phone.

Advice is greatly appreciated. Thank you.