Sudden spike in data usage

I just got off the phone with an agent after disputing my current data usage trends and I'm fuming. I have been with Comcast/Xfinity for YEARS. I have never gotten close to reaching my data limit. I've never gone over 700GB in a month, ever. Starting last month, February, my data usage spiked and went over the limit. We're now 13 days into March and I received the 90% usage notification. There is absolutely no way. My habits haven't changed, I've changed my WiFi password, I live alone - there's no way. 

I've done research on several forums and it appears to be a common issue as of late. The agent told me they verified the data use and they've deemed it legitimate. Meaning, I'm responsible for paying whatever overage charges I receive. But wait! "You could upgrade to our unlimited data plan to avoid overage charges!" 

I refuse. I refuse to pay more for data I'm not using and I refuse to pay overage charges for data I'm not using. Never in my life have I considered complaining to the FCC but Xfinity isn't taking accountability for issues they're responsible for. The evidence is damning so I think it might be worth it. 

Either that, or I'm changing services immediately.