If your current subscription to Google Play Music is expiring and you have no desire to extend it, do as follows to cancel Google Play Music All Access subscription right from your Android device:
1. Open the Play Music application on your Android device
2. Tap the 3line icon on the top left and head to the Settings.
3. Under the General settings, tap the Cancel All Access option
4. Now you are redirected to the Play Store and the Google Play Music page
5. Under the Uninstall and Open buttons, find the Cancel button (There you can see your current subscription status and your next payment due)
6. Do as instructed and your Google Play Music All Access subscription is canceld