I know this game is very old now but just so people are aware, your online rank is tied to your save, not profile. If you hit level 50 and thought you couldn't get this anymore, you still can.
Just move your save to a USB or other storage and start a new save on your HDD. This will reset your rank back to level 1 allowing you to get the achievement. Be aware though that it will also reset your current progress towards the achievement so you will start at 0/10 wins.
Once you get your 10 new wins (and ach), you should go back to using your old save again so you won't have lost any progress toward any other achs. I did this myself so can confirm it works.