Excess Data Usage - Not my Fault

I have used about 200-300 gb per month in the past. Suddenly in March it jumped way up, and with 10 days to go in April I am already at 1.6 TB. I contacted Xfinity (why can't they use people you can understand?) and talked to 3 different people for over an hour and it solved nothing. That was 2 days ago when I was at 1.3 TB. Now I see I am being charged $80 for the overage. I am bout ready to leave Xfinity and go with another carrier. We have been a customer for 13 years. This is so MADDENING!!!