daytime data used up instead of night owl

I waited until midnight to start my downloads as usual since I use my day time data for school work. Yesterday I had 872 MB left for day time use, I used my night owl data and it was depleted around 1:50 am. So I went to bed, when I woke up and tried to access the internet it said I was out of data. So I checked my balance and I only had 10240 mb for wifi or whatever, this is not right as I can't use night owl data during the day when my day time data has depleted, so why does my day time data get used during night owl time.