Ranked games - Promotion Series - three games win but promo says two games win one game loss

Hello,

I got into promo games from silver I to gold. But somehow after my third win in a row instead of getting into gold my game was listed as a loss. Well I know I won and my match history also says that I won. So right know I'm kinda reluctant to play another ranked game to possibly get another weird loss record instead of a win.

I have literally no idea how this happened so I can provide no description on how to repeat this.

I would post a screen but I highly doubt that would help, so if anything my ingame history says it pretty clearly (my ingame nickname is: aCup of Tea)

So anyone knows what's happening?

Thank you.

EDIT: I even have that hot streak icon for winning three games in a row xD