Not received 15gb night time data??

Good Day<br> <br> on the 21/03/2016 I got the 5gb and 15gb night time data for R99 promo from Cellc<br> so last night I wanted to download from the night time data (00:00 - 06:00) a 4gb file this morning when I woke up the file wasn't completed and when I went to check I received an sms that said my data has been used up but when I go to the Mifi web management page to usage it said my usage is at 7gb? I assume that the data was deducted from the normal day data and not the 15gb nigh time data please can you contact me to clarify what is going on.<br> <br> Kind Regards