10 GB data vanishes in a day

I am so livid with Telkom. I purchased 10GB + 10 GB LTE data last night (28 January 2018) after 8pm and used it for about an hour and switched off my modem. I was at work the whole day today with no one using the data and it’s finished. this data comes with night shift data so when you switch on your modem after midnight the data that is used should be the night shift data. So how the hell does 10 GB of data finish in a day. This is the second time this is happening to me last time I lost 20 GB of data the same way and Telkom could not explain what the hell happened to my data. Data in South Africa is so expensive and we get milked out of our money and customer care is so horrible