So basically my rank was like around 800 but i never got the rank achievment , then i logged off for the night and came back on the next day to find that my rank had jumped to around 8k ... And now each time i win matches it keeps increasing... now its at around 9k

Ranks act weird sometimes, but usually get back to what it should be the very next day.

The ranking system also depends on who you played [and what their statistics are], specifically.

Oh ok , Thank for the info Bolty.