How can I get a report of data usage by device or by MAC address?

I'm sorry, but you seem to have completely missed my point. I have the account wide data usage numbers. I am looking for device or MAC specific numbers. Some device is increasingly using more and more data and I am trying to find out which one. Even if I were to turn them off one by one, that doesn't help me find historical data usage, or track changes in use over time. 

Is there a way to see device or MAC specific data usage information?

@NoMoUserNames sorry for the confusion. Our gateways do not track individual device usage or Mac address only overall data usage. There are some third party devices on the market that can. If you'd like you can use our device info page to check compatibility once you've found a device that is capable of reporting data usage by device or Mac address. 

That's such a basic security function, I really don't get why it's locked out. Or actually I DO get it, because xfinity is happy to charge for data overages and has a clear financial incentive to keep me in the dark, even if makes my home network less safe. 

I switched from using my own device to an xfinity gateway years ago in part because of the claims of "access to value-added services such as xFi". But what I am hearing is that I am paying extra per month and in fact getting less for it, AND it makes it harder to detect and diagnose possible security threats, AND when I have data overages, Xfinity also gets to charge me extra for that too.

Real great service...

@NoMoUserNames being able to track data usage per Mac address would be an amazing feature to have on all gateways and accessible through the app. May I ask are you suspicious that there is a threat to your network? We have options to assist with protection. For example, multifactor authentication, scans for malware, and firewall setups. For more details see:

• https://www.xfinity.com/support/articles/top-internet-security-tips
• https://www.xfinity.com/support/articles/computer-virus-protection

We also hope to help customers avoid overage charges through our unlimited data plan option or adding xFi Complete which provides unlimited data. Our new nex-gen promotions also already provide unlimited data. Howvever, should you go over on a plan that does have a data cap, we offer a courtesy month credit. 

"courtesy month" is a benefit for Xfinity Internet customers that allows one month of exceeding the 1.2 TB data limit without incurring overage charges. This courtesy is available once per 12-month period. If you exceed 1.2 TB a second time within that period, you will be charged for overages. You can track your courtesy month count through your account's Usage Meter. If you do not exceed the limit again within 12 months, you may receive another courtesy month.

For more details see: https://www.xfinity.com/support/articles/data-usage-exceed-usage