Hello marioluigi: I see this is your first post here on PC. So... welcome to PsychCentral!

I hope you find the time you spend here to be of benefit.
I'm sorry you are struggling with these difficult memories.

My situation is quite a bit different than yours. But I also struggle with memories of things that I didn't think that much about at the time, but that came back as you say "like a freight train" later on & that still consume me day-after-day. So I believe I have some idea of what you're going through
Unfortunately, we can never go back & change what occurred in the past. (You probably didn't need me to tell you that.)

And trying to block or in some other way get rid of intrusive thoughts only makes them keep coming back stronger & more frequently in my experience. (Since I'm an atheist, I haven't tried prayer.) So the only alternative at least from my perspective is to learn to allow intrusive thoughts to come forward, to accept them with lovingkindness & compassion, & to allow them to simply fade at their own pace.
There is a technique I employ for addressing my own intrusive thoughts. It is referred to as "compassionate abiding". Here's a link to a description of the practice. Hopefully it can be of help to you too:
https://mindsetdoc.wordpress.com/201...e-abiding-101/
Here are links to a bunch of articles, from PsychCentral's archives, on the subject of how to let go of the past. There are quite a few of them.

But each one is short. So it's not as much as it may appear:
https://psychcentral.com/blog/learni...ys-to-move-on/
https://psychcentral.com/blog/let-go...give-yourself/
https://psychcentral.com/blog/how-to...of-letting-go/
https://psychcentral.com/lib/depress...tive-thoughts/
https://psychcentral.com/blog/lettin...ful-over-time/
https://psychcentral.com/blog/9-ways...tuck-thoughts/
https://psychcentral.com/blog/how-to...nful-emotions/
https://psychcentral.com/blog/what-r...your-life-now/
https://psychcentral.com/blog/learn-...give-yourself/
https://psychcentral.com/blog/start-...-inner-demons/
I hope that you will be able to find a pathway to deep peace within...