There suddenly was an increase in data usage

The data usage hasn't changed in my household, yet xfinity has said I'm using over the 1.2 TB since July.  I see that there are many other customers who have experienced the same problem.  The problem is with xfinity. I have called twice regarding this issue and was told I would need to upgrade to the unlimited data plan.  One agent told me I had used 75% of my 1.2 TB in one day in July.. one day!  That isn't possible.  Xfinity is the problem.  When will this end?