My 1GB Data depleted without me using it,600MB for 1 day not 5 hours

Yesterday at 06:07 I had purchased 1GB for R17 for 7 days.During the whole day I was at school and I wasn't busy with my phone only at break I was.When I came back from school I was on my phone until I got a notification saying I have 510MB remaining when I didn't download anything on YouTube or Play Store then 2 minutes after it's said I have 205MB remaining without being on any app for at least a minute then next thing you know my data was gone.To add on that note 19:11 I purchased 600MB for R9,50 for 1 day which I try to understand why at 00:00 it's gone when a day is 24hours not 5 hours and this is getting out of hand this is the second time I complained about Telkom.So Telkom you better fix this mess up immediately.