Spotify runs all day even after I close the application and optimize my phone . . .

[user-removed]

Plan

Premium

Country

United States

Device

Samsung Galaxy Note 9

Operating System

Android Oreo

My Question or Issue

As was stated in the title, I closed Spotify after I got through my morning routine only to have it stay on in the background and stay in my pull-down notification bar. I went into my settings and device management to optimize my device, which should have stopped Spotify from running and removed it from my notification bar, but it still remained. How do I close Spotify when I'm ready to close it so that it doesn't gobble up my data, my battery, and my memory?