Not getting the internet I paid for, but going to be charged $100 to fix it

I did self install for my internet and I pay for 800 Mbps. Testing is giving me 16-90 Mbps through speedtest.net as well as Xfinity's website speed test and the Xfinity app.

I am going to be charged $100 for a tech to come out to resolve this because I did "self-install" which was the coaxial cable, the Ethernet cable, and the power plug. How is this a ridiculous $100 charge? I live at an apartment complex. The line was ALREADY set up. There was nothing for them to "professionally" install.

I feel like I should not be charged this fee and on top of that, they can't even come out for over a WEEK? I should be prorated fees for not having the speed of my internet that I pay for and having to wait this long to get the issue solved, not to mention having to miss some of work over it which costs me money.

I am beyond infuriated about this. I am using YOUR gateway modem/router combo, not my own. I'm hardwired in. And you're forcing a charge onto me to fix something on YOUR end. I haven't even been using this internet for a month.

All while using 4% of the internet speeds I pay for. I pay you $75 a month with a 2 year, new customer plan and this is what I get in return? Ridiculous.