Am I being stupid to feel upset over this

So basically there are two guys at work who are both friends, both have recently arrived here from the same country I believe.

One of them started to behave inappropriately towards me, though I am in my early 30's so I am able to handle it, even though it makes me uncomfortable.

One day this same guy tries to get my teenaged coworker in his car after work, he also did this with me (he would drive up to me on the road and I'd feel pressured to get in) and would text me sexual things after dropping me near home. I told her not to get in his car and explained his behaviour and she told me his friend had also tried to do the same thing. These men are around 30 or older.

I reported it to my manager and she said she would be mindful about not having us work with them In the future and that she would talk to the female coworker about it as well. I was put to work with one of them today. I asked her about two weeks later if the manager had spoken to her about it, she said no. She also made a comment along the lines of oh I'm pretty sure you're telling the truth, some people lie about this stuff..

So not only did my manager effectively do nothing, the girl I was trying to protect considered that I may be lying about everything. Plus I made myself look like an idiot to my manager bringing this up, and the sexts etc.

Do I just not bother trying to protect people in the future? I feel like I'm a bad person when I was just trying to look out for someone, lol