Weird situation on Ranked promo

So I was playing my promo for Plat 3, I had 1 lost, I started second game, and because of problem that I couldn't fix (power cut) I left game early, but my team won without me :D , I tough that will count as win in promo, but It didn't even it says in my match history I "victory" still I lost promo :D Not sure if that should work like that, but I would like to know :D BTW, I don't care for promotion, I know its my fault for "losing", I just want to know :D
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