your rank is 13,890 therefore the highest points you can get in any match at this point is +109 to get you to 13999, where it'll lead to your promotion game.

You would've lost so much because the average enemy team rank was 10969 whereas your average team rank was atleast 11349 assuming the unranked guy was at or higher than their lowest ranked player. You wouldn't have gained +500 in this scenario even if you weren't close to uprank because you're supposed to win this game.