I Didn't Change My Number appears on Happier Than Ever, the second studio album by Billie Eilish, released in 2021 and written with her brother Finneas O'Connell. The track opens the album's second half with a direct address to a former contact who assumes she has cut them off. Short excerpts of the opening line later circulated on social video platforms as a standalone audio, detached from the full song and reused in edits about boundaries, confidence and not replying, keeping the lyric familiar beyond album listeners.