Promo round Lost after DC (we won the match)

I was just in my first promo to reach Silver 2, DC'd at the end of laning phase, had to wait for my internet to restart and reconnect, but when I got back we won the game. Match history says "Victory" but I still have an X on my promo series like I lost. Game also gave me a D- like I left but my score is 6/2/5 (all except 1st kill happened after I returned). I didn't intentionally leave and I even managed to get back in and finish the game strong so why am I being punished?