No Promotion After Winning Series

I won my series for Platinum II (2-1), but instead of getting promoted, I was granted LP instead. Now i'm left at Platinum III 100 LP

http://matchhistory.na.leagueoflegends.com/en/#match-history/NA1/214272679

As you can see in the link above, I lost my first series game with Orianna and I won the rest with Lulu, which would've brought me to Platinum II. The only conclusion I can come up with is that there was a maintenance for the log-in issue right after my last ranked game.