I am having the same problem. It is really annoying when I pay to listen to music but it keeps getting undownloaded.
In this case, we'd recommend deleting your offline devices by heading here. Then, uninstall the app and remove the SD card (if applicable). After this, reinstall the app following these steps.
Let us know how it goes.
It's been a while since the last reply. Is everything ok now? If you still need help, feel free to get back to us. For now, we'll close the post.