Before you decide someone is scripting, please consider this quote

"Any sufficiently advanced technology is indistinguishable from magic." -Arthur C. Clarke

I will repurpose this to accomodate scripting;

"Any sufficiently skilled player is indistinguishable from a scripter." -DTN

Sure sometimes it's obvious, and this applies less and less to people the higher elo you go since you're better at recognizing true skill, but before you decide someone is scripting please first consider they might just be so much better than you at reacting to and anticipating your moves.

If you truly believe they are really cheating, there is a report option for that. Do not sit there and harass and accuse them, just mute and report them. It's Riot's job to investigate it and they are much more able to verify it, so leave it to them. If you decide to make a scene (which won't improve the chance they are punished) you just become a problem to the other players and may be punished for it.

If you were able to take a video of the cheating which would prove it, provide a link to it in your report description. If you were unable to report it then, you can submit a Support Ticket using the category I have a question > Game & Features > General Questions.