Sudden unusually high data usage

We have been Xfinity customers for a number of years and our internet usage has consistently been hovering around 500-700 GB on average per month. I got a notification yesterday that we have used 1135 of our 1229 GB with 5 days left in the month. Our habits and connectivity haven't changed this month and there were 4 days we weren't even home this month. There is no way we almost doubled our usage.  I called Xfinity customer service and all they told me is that they can only see my usage by month, with no additional details or breakdown to get to the bottom of this usage, which is unacceptable and does nothing to help get to the root of this issue.