Need help understanding what happened to my bill after taking advantage of the new 5 year price lock for internet

About 10 days I took advantage of the 5 year price lock offer for internet.  Via the online configurator I picked the 500mbps plan which showed $0 month change from my current plan but gave me the 5 year lock package.  I made absolutely no other changes.  I took advantage of the new equipment, the gateway, that the chat agent confirmed was included free with the 5 year package.   FYI, I had to involve a chat agent because when I attempted to check out the system kept saying there was an error.

The original chat session and order confirmations all said the same thing that my new monthly bill would be within a few dollars of my current bill.  To my shocking surprise today when I went online and clicked on the upcoming charges I saw that I was going to be charged around $75 more per month.  Every bit of info I had said my bill would remain roughly the same.  I then saw another area in my account that said my bill would be about $45 more.  So, conflicting information within the Comcast billing system.

Today I started a new chat session which did not go well trying to explain that I had an order confirmation via email and other sources that showed my monthly pricing was nearly unchanged.  After a long time of trying to get my proof explained the agent said changes were made and I should once again see what I had previously thought I was getting.  It would take 24hrs. 

Now I am skeptical and very very concerned.  This should not have happened.  I am still recovering from the $75 month increase shock.  I had confirmation yet the billing system had some other agenda.  I had absolutely no intent to make any changes that would have resulted in additional charges.  The whole point of even attempting the 5 year offer was just to save money in the long run, not cause me to pay up to $75 more per month.

I know this is asking a lot but I would like an agent to look into this and help me understand what went wrong.  I am counting on Xfinity being truthful with the order confirmations and not make drastic unexpected billing changes after the fact.  I can include in any conversation, DM..., all chat transcript summaries, order confirmation summaries, and screenshots of the whole process.

I had gained some respect for Xfinity lately as I saw attempts to be more consumer friendly by offering deals, perks, and customizations never offered before.  But now that extra respect has faltered.

Thank you.