Level Went Down Upon Level Up?

I am level 19 ( should be 20 ). Upon getting my daily 400xp for winning, my level didn't increase to 20 as it should have, as I had more than enough to level up from that 400, but instead went back down to 19. When I went to check my xp it showed 1824/0 XP in my xp bar, and after winning another game it just restarted the whole level. How do I fix this? Leveling up a new account as a returning player is literally the worst experience I have ever had in league and I really don't want to have to add 1 more level onto that shit.