A simpler fix is to stop apps from using mobile data for music at all.
On iPhone, go to Settings, then Mobile Data.
Scroll to each music or video app.
Turn off mobile data for them.
Now those apps work only on Wi‑Fi.
You avoid surprise data loss, no new app needed.
You can also set Low Data Mode in Wi‑Fi and Mobile Data to slow background use.
This works well if you stream at home, then listen to already cached songs on the go.