Depleted data and the resulting ******ion

I just recently upgraded my contract at MTN, increasing my monthly data bundle from 75MB to 300MB. In addition, I purchased a recurring 1GB data bundle so that I wouldn't have to worry about data again, since I am on wifi most of the day in any case. I had my new contract for a little over a week when I get an SMS telling me that my data has been depleted, and I am using data at out of bundle rates. I found this very pecu****, as I was at home on my wifi at the time. According to my phone, I've only used 507 MB - meaning I should still have another 800MB. When I called to find out what happened to my data, I was told to \log a call to investigate". This takes 3-4 working days and since it is now a Friday"