Rank shown on achievements card is based solely on your qi vs qi of other people with the same belt as you.
Rank ingame is split into global rank and mod rank and uses elo system en.wikipedia.org/wiki/Elo_rating_system
To improve your rank you must consistently win games. If you often play against alts/new players and lose, your rank will drop very fast. This must be the case for you. Your elo points are deep below 1600 (base) which new players start with.