So I started delivering lettered to get the achievement and everytime I look at gamecenter to see how many letters I delivered it stays the same 33 even after delivering like 10 letters it still says 33  

In your profile, go to the gamecenter tab and make sure "Send scores to Gamecenter" (or something like that) is checked. Afterwards, you might need to kill someone for it to send the score.  

Dosnt work