How do I remove "Phantom music" from my phone?

I have the program "Mix" that came pre-installed on my android phone and every month I like to clean out my playlist and start fresh by manually deleting the files through my computer, and then clearing Mix's cache/data (it starts glitching out if I don't, it doesn't seem to deal well with massive file deletion). But starting last month, after I do this, the music is still there. I tried searching through my computer all of my phone's internal and sd card files, and did not find music anywhere. The only way I can remove it now is through the mix program itself, one song, album or artist at a time. I would like to know if anyone can tell me what's going on and how I can delete all these songs from my phone?

details on software/product:

Mix v5.2.8.1.0431.0_lite
phone version- Straight Talk androind hpone model number A571VL
configuration version - G15.AOT.A571VL.0
PROCESSOR iNFO-QUALCOMM TECHNOLGIES, INC. msm8909
Android version - 5.1.1
Baseband Version-1.1.c1.1.2-00005-8909_GEN_PACK-1
Kernal Version-3.10.49-g5bece6a-00002-g9e227ac-dirtyandroid-bld@Perso216 #1
Build Number vCBLD

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