Go to your phone’s setting and check the data usage screen.  Does it show an app or service that has used a large amount of data unexpectedly?

You also mentioned you were charged for data overage.  Did you not get a text that your have reached your data limit and your data paused?

This happened to me as well! Very frustrating. In one morning 13 GB of data was used while I was at work. This has never happened before. I ran out of data with in 3 days of my monthly renewal. I have 15GB of data and I have never used it all before. I haven’t changed anything about my phone. I am debating about changing to Public Mobile. I also can’t get a hold of any customer service representatives to help me with this issue. 

To be clear, koodo cant make your phone use data so changing providers wont solve the issue.  Did you check your phone’s settings to see what is triggering the data usage?

Here is an example for my data usage