Best answer by The Magic Talking Wall
Only your phone can tell you what used up this amount of data. Check your mobile data settings to find a list of apps that connected to data during the current period and you'll likely find the culprit.
Koodo only measures the volumes as communicated by your SIM card and measure them against your plan details.
A healthy habit to take is to disable data when you don't need it, like when you're connected to wifi. That will prevent all unwanted usage.