Application Control: Application / SPOTIFY,PANDORA
Username / blabla
Action / Block

That did the trick. For some reason when trying to block by "Application Category", the block registers as being applied, but the music would still stream. If I specifically blocked the "Application" followed by listing the desired applications, that worked.

Is this by "design"?

I didn't find the right solution from the Internet.

-References
-https://forums.untangle.com/application-control/37837-streaming-media-category-issues.html

-Creative Product Video