Can a human being explain discrepancies in my plan costs and data usage?

I have had Xfinity home internet for years.  Internet quality has been bad.  Customer service is even worse.  Biggest problem is that there have not been alternative options until recently (finally Verizon covers my address, cannot wait to explore that).  This month for the first time ever I got an email saying we were at risk of overage charges for home internet.  We pay $123/month, so needless to say that was a substantial concern.  Always figured that was unlimited home wifi...  I tried to connect with an agent and simply could not.  There are two factual discrepancies that no one from Xfinity has been able to help explain to me.

1. I started getting these messages that our usage was beyond our plan and would incur overage fees.  Then I looked at our "data usage" as measured by Xfinity over the past 12months.  The first four months averaged 670mbps, the next four months TOTALED 0mbps, then it went from 0 to 196 to 720 to 1,349mbps.  This is all with no change in behavior on our side.  No new devices that we're aware of.  I work from home and you're going to tell me we used 0mbps for 4months?  Must be true if you're going to charge us overages for the "1,349mbps" we used this past month.  You have lost all of my trust with this...  

2. I looked online for what it would cost to get Xfinity if I was moving to this address and it was $65 for 1Gig locked in for 5years.  I'm on year 3 of 800mbps and my bill went from $113 to $117 to $123/year.  And my service is horrible, to a point where I have to use an Eero mesh system to make it even manageable.  I know you cannot reliably measure our usage, but even if we let you make up whatever usage numbers you wanted we would still be under 2Gig and according to your website that means I would pay a max of $85/month.

I would like 1) someone to explain to me how the data usage could be so wildly inconsistent and factually incorrect, 2) to be switched to a plan that is actually market rate, 3) to be credited back for the fact that I've clearly been so criminally overcharged for the past 4 months.  This seems like a BBB issue... outrageous.  And I wouldn't be quite this frustrated if it weren't next to impossible to get in touch with a human being that's actually empathize with me and provide actual customer service...

Less important but it seems clear to me after dozens of attempts that as soon as I hit "chat with an agent" on the "Xfinity Assistant" that it just kills the conversation... is that not a real button?  Spent 10minutes begging that assistant to help me and for nothing.