Players not filling the roles they are assigned

Dear Riot,

Today I was in the Final Promos for my Top lane role when I encountered a player who did not want to fulfill the role he was assigned. The encounter went something like this. The player asked if he could go Top. I as nicely as I could replied something like "If it were any other game I would say yes, but this is the final game of my promo series so I am going to have to say no". I then locked in Garen. This player then decides to lock in Renekton, remove Smite from his summoners and as the game started follow me into the Top lane where he would do everything he could to take as much CS as possible until I figured it would just be better for me to roam the map as at this time the enemy team had started to group. Now Ill be honest, normally I would not write a post about Trolls in a game that seems to be plagued by them, but this situation really bothered me for one specific reason. After the game was done, and the Renekton had racked up a nice 0/5/3 score while the whole time typing at us to "report him". The score board said that I had traded positions, that I would have my positional match making system disabled if I were to continue doing this. It really felt like a punch to the gut after having to play that as my final Promo game, and your in game systems claim I am the one who tried to switch positions. Maybe I am over thinking it, and the 4 reports my team mates plus any from the enemy team we were lucky enough to get would clear up the confusion, but I got to say Riot. It is really worrisome when your in game systems that seem like they are put in place to catch and punish the people doing this are getting it completely wrong. Thanks for reading, and I know its probably unlikely, but would really like some feedback from a Dev on this and get their thoughts on this situation.

Repsectfully, The Goat