they do not raise me in rank by winning

When I play the Assassin mode many times they do not raise me in rank and they always lower me a lot when I lose, not only did I pass by once.

It can happen, do you ever leave the matches early?

Have a read through the Matchmaking Feedback topics that are pinned in the Matchmaking forums. They give in-depth explanations of the ranking system, if you still have any questions feel free to make a post in the latest pinned thread. Link up some of you recent games as well if you have queries about what happened in specific matches