Downloaded songs are not playing when i have no internet connection.

Why is it that I am paying my 5.99 monthly and whenever I download music onto my device (iphone 7+ ios 14.6) and try to play them without wifi or data.. actually my whole library only plays for 15 seconds on each song and stops there!? Its as if they aren’t even on my device. If I am paying for music I should be able to listen songs offline if I added them to my library and downloaded them. It’s freaking annoying. And as soon as I have internet connection then I can play any song i want.. as if I’m still streaming downloaded music. Please fix this or I’ll go back to streaming music for free on Audiomack. Jeez