If you truly need offline MP3 files for a feature phone or basic MP3 player, consider to MP3 for personal, educational, or review purposes—but only for tracks that are in the public domain or uploaded by the official artist with a "download" allowance. Alternatively, buy MP3s from Amazon Prime Music (download included in Prime membership) or Google Play Music (now migrated to YouTube Music; purchase tracks individually for ~₹15-20 each).