How to report after match harassment

Is their any system for reporting players harassing you outside of a league of legends match? A player on the other team did this. Is it okay for them to harass you by adding you and proceeding to talk trash about you and your loved ones? I ended up blocking the person because he tried to act all nice after harassing me. I have screenshots if there is a place to report this to. Thank you for spending time to read this.