Yes, you will never get a response from a production company if you are an unagented writer. I mean, never say never, but.
If you did not go through a California film school where you got plenty of contacts, you can work hard at creating a community of other creatives like you, which tend to share the wealth with each other and climb the ladder together.
If you don’t have that, you can start on an egalitarian platform like the Austin Film Festival or any of the other big competitions, or a tracking board. Going through the vetting process of a competition is a cheap way to get your script some credibility and a leg up. If you do well there, then production companies will contact you!
There are one million scripts for every need, and nobody has the kind of time to pick you out of the krill of unsolicited scripts, is what I’m saying. Everyone is looking for a good script, but there is such a small pool of them that it’s like a needle in a haystack. Make yourself into a much bigger needle.
I do not hope that this is discouraging, but that it gives accurate information that you can use to succeed.