This is what I have never understood about calling congress people. Why would they listen to a random person? If you have some clout or are an expert on a niche issue sure. But I just feel like if you’re a nobody why would they trust you.
The rep isn't going to listen to you specifically - you get a form letter back (sometimes years later), and the only thing that matters is the issue and whether you're yay or nay. But because so few people call in, it makes your opinion (on that issue, at least) weight much more highly than the average voter.
It's one of the ways they keep track of what their voters care about.
This was from a friend who interned there 20 years ago, things may have changed.
The dynamics are different with proportional representation. You care more about keeping your core supporters happy, because the random people opposing something loudly will probably vote someone else anyway.