Billing 100 installation fee

I just moved into an apartment that is fairly old. It surprised me no one has used Xfinity before. All previous residents used AT&T I guess. I chose Xfinity because my friends told me it is stable in Michigan.

After I got the machine, I tried all the coax outlets continuously for 2 days, but no one was working. Called customer service, and they told me they could send me a technician after 5 days, and they told me, "IF IT'S NOT CUSTOMER'S FAULT, XFINITY WILL NOT CHARGE ANY MONEY." Eventually, the technician found it was because the coax cable connected to the outlet was not the correct one using their testing machine. And then I was charged 100 DOLLARS for this. Called customer service again, and they kept telling me this was a valid charge...... I am not the apartment owner, I don't have the testing machine, and I don't have the design diagram, how did I know there was another coax cable hidden in the outlet........Really disappointed about the service here.....will probably consider other cableless providers next time.