Xfinity Internet Data Usage not accurate

Last month, my Xfinity app stated I only used 77 GB of my overall 1.23 TB of Internet Data. Oddly, it stopped updating sometime early to mid last month. It did reset, though now it states I have used 0 GB. I tried checking my Xfinity account on a computer, though it still states the same amount.

I tried reseting my modem, though nothing changed. I called Xfinity customer services, though they informed me it should be accurate. I have doubts it is accurate, and that there may be glitch causing it not to show the actual data usage. 

I tried looking up how to send a direct message for support, though it seems I need to start a public forum in order to do so. To Xfinity Support, please assist myself with this technical issue. I would like to have this issue resolved as soon as possible. Thank you.