My mini SD card on my Samsung Galaxy s5 won't play music, what is wrong?

I recently bought a mini SD card for my Samsung galaxy s5 and it's reviews are mostly bad. I first moved all my music onto the mini SD card and it all worked fine. I tried to download some more songs and move them to my mini SD card with the rest of my music. I did so and it worked great, but then I tried to play it and it didn't play. After many hours of trying to do IT OVER AND OVER again, I tried to move a video on the mini SD card and, surprise, it didn't play! What the hell is wrong with the thingie?! I wasted 50 dollars on it for 128 gb and Its working like crap. Did I just get cheated?! What do I do? Can I fix it? Thanks.

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