I'm pretty sure OP meant that the day before the flight was when they discovered the mistake in the amount charged, not that the hold was made the day before. I conclude that the request to fix the problem was made several days (well over 24 hours) after purchasing the hold (OP, please clarify). Note that OP originally stated they requested a refund, not a 24-hour refund. Posters started discussing the 24-hour refund policy but this was never really the point.