At most places, 95% of the customers are dumb as rocks. And 95% of the support staff is also dumb as rocks. So they're conditioned to assume everyone calling in is an idiot, and it's very likely that whoever you're talking to is not equipped to understand what you're saying to try to convince them that you're not.

My favorite instance of this was with an ISP that rhymes with Bombast where it was very clear that the modem wasn't getting a signal. The lights indicated it, and I was also able to connect to the modem's internal monitoring and see that it wasn't seeing anything on the line. The support agent kept asking me to reboot my computer.