Make it do a WriteLn of whatever text you're getting from ReadFile followed AND preceded by '=' (to make sure there's not like some weird unseen characters). It should say =9= if it works right.
Make sure kill[ID] is an integer.
Also I recommend that you should make one file for ALL players. Also, I would make it write the player's IP as well as the player's name (so that someone else can't login with the same name and get points). I would recommend making a .txt file called "PlayerKills.txt" and that it looks like this:
45.178.175.33
someplayer'sname
34
45.34.28.111
someoneElse
16
94.122.101.93
AnotherPlayer'sName
67
So you'll only have one file!
Also, use enter to separate each line. Don't do 34.3.65.111-playername-23 because then if the player's name contains the character "-" then he can screw up the file (Players, I believe, can't have an enter-symbol (#13) in their name).
Hope that helps!