The first Layers of Fear was pretty spooky, very PT inspired. The second one was decent too, but not as scary.
Outlast is the standard I hold walking sim horror games to. I can speedrun through it now since I've played it so much, but the first few times were terrifying.
Some people have mentioned Amnesia, so I'll throw in the recent iteration with Amnesia: The Bunker. It's like Alien: Isolation in a WW1 setting.
Speaking of which, Alien: Isolation is probably no. 1 for me. Between the alien, the androids, and even other people, that game is very stress inducing.
If it's any consolation, Amnesia: The Bunker has a different AI than the previous iterations. I mentioned it's like Alien: Isolation, and the monster works very similarly, like reacting to how much noise you make and stalking which parts of the bunker you're in. Most items with every run are also randomized, so you can't memorize where to pick up supplies. (You can also customize the difficulty, which I thought was really cool.) But if you've already tried it, then my point is moot lol.