8ta / Telkom Mobile
Dara contract depleted

I have a 60GB 60GB once off data contract for the second year. Last year I only used 20GB the whole year. This year it was depleted within a month and a half. I contacted the call centre more than 10 times now, logged 3 formal issues and each time I get the same 'easy' answer: "you used your data".
Nobody is actually helping understand how I could have used 3GB per day, whilst at work. I have ADSL at home so never used the data at night.
I cannot use their product again or buy more airtime until I understand how the data got depleted.