high data usage spike

I'm almost certain xfinity is using high data usage as a scam to make customers pay more money for their service. The forums are littered with similar posts and 0 resolutions.

I've spent over a month on many 1.5+ hr calls trying to get some information from the xfinity team. i've been kicked around repeatedly by the billing, support, and "technical" teams. 

I started my calls to xfinity since the end of June as soon as i received my first notice of high data usage. My first callback from the quality assurance team was July 29th, an ENTIRE month later. On more than one occasion, the technical team and the billing agents assured me that i would not be billed. Here I am now looking at a $100 extra charge and most likely another $100 overage charge in August.

My billing surged from <600GB/mo for a whole year to 3TB starting in June, 6TB in July, and already exceeded 1.5TB for Aug. For a rough reference to how much data that actually is:

Assuming the average movie is 1 hour 56 minutes long, 1080p resolution, and stored as a h.264 MPEG4 video file, it would take approximately 5.085 GB of space. You would be able to store about 983 movies in 5 TB, or 1,901.02 hours

There are 730 hours in a month, this is me streaming ~3x 1080p videos around the clock for an entire month, which is an absurd amount. I was also not home in July for half of the month and I had the largest data usage month on record. 

Even after many 1.5+hr calls with xfinity, the only advice I received is (outside of the typical restart your devices and change your pwd):

• pay more money by upgrading to an unlimited plan
• pay more money by renting xfinity equipment ( i currently use an Arris surfboard S33v2 - a very commonly used and xfinity approved modem that's only about a year old)
• You probably have a virus
• upgrade your modem - i cannot upgrade my modem, because Arris documentation states it must be done by the service provider. however, xfinity says they cannot upgrade my modem. an agent later told me i don't have to upgrade my modem?

I closely monitor the traffic and devices on my network and nothing has changed since before the spike. My router shows i'm using very little internet and all devices are accounted for every time I check.

My network topology is Modem (arris s33v2) -> wifi router (asus TM-AC1900) -> extender (TPLink RE550). I have a couple of home devices (2 echos, 1 google home, one nest camera, some sengled lightbulbs + hub), 2 macbooks, 2 iphones, 1 samsung tv - nothing out of the ordinary and has been this way for years. and again, i monitor the traffic coming from the router and it's normal usage. I even tried disabling all devices and re-adding them one by one and no surprises.

At this point, I'm out of ideas other than just swapping providers or coughing up the money to xfinity. any advice or help is much appreciated. and if Xfinity support ever sees this, please stop trying to make me go away to close out your support tickets and help me actually solve my problem!!