You can't win a game on time if you don't have mating material on the board. Since your opponent ran out of time and you only had a king, the best you could ever hope for is a draw so that is all you could get.
It is called Draw by Insufficient Material. Read the last paragraph of the following.
https://support.chess.com/customer/en/portal/articles/1444798-how-do-i-claim-a-draw-
As to rating changes, it depends on the ratings of the players, how stable those ratings are (the Rating Deviation or RD) and the outcome of the game.
https://support.chess.com/customer/en/portal/articles/1444777-how-do-ratings-work-
Hello,
I played a Game against "Bingabel" today and should have won by time (+25xec). The game was rated Remis, because of to less material?
Three or four days ago, I played against a player with only 5 ELO points more. He won and got 9 points?!
Is the new chess system in Beta-Mode?
Your help is much appreciated.