Since the latest update, there is a new requirement.
To reach the first league (Bronze) you must be over 2799 COGs. So basically, hit 2800 COGs and your achievement will pop when you are put in bronze league.
The other solution is now out of date, and the achievement will not pop at 1600, 2000 or 2400 cogs.
A win/loss nets you approximately a gain/loss of around 25/30 COGs.