[Pottus]

new level = GetPlayerScore(playerid), string[32];

Should probably be, new level = GetPlayerScore(killerid), string[32];

You also have these lines mixed up a bit....

KillsLevel[playerid] = CreatePlayerTextDraw(playerid, 499.0, 101.0, "Kills: 0/0\nLevel: 0")

format(string, sizeof(string), "Level: %d\nKills: %d/%d", level, kills, level * 50);

You want.... format(string, sizeof(string), "Kills: %d/%d\nLevel: %d", kills, level * 50, level);