Prime vs unlimited

So i've been using prime video for a while Now, and i wasn't aware that comes with Amazon music, so i downloaded the app. Apparently it's the same account and i am learning to use it but i can't figure it out if the unlimited version is better or it's the same, cuz i can't play some songs but i can download others, and they offer me to buy the unlimited despite i am using a prime version. What's the difference? I did something wrong?