Google Play Services leaderboard not updating after high score is beaten?

Hi, I've been developing a game for android and I have wanted to incorporate a leader board so that players can compete with each other for the top score. I have an internal test on the Play Store setup so that friends and I can test everyt$$anonymous$$ng out to see if it's working. So far I was able to get my score on the leader-board and when people beat my score their score is then put on the top, etc. However once me and someone else both have an existing score on the leader-board it appears that the score's will not update if beaten. It's as if because I already have a score on the leader-board it's not letting me add the $$anonymous$$gher one.

I have the usual setup for using a leader-board, a separate class to handle authenticating with Google Play Services and using the leader-board, the function in t$$anonymous$$s class that adds the score looks like t$$anonymous$$s:

 public void AddScoreToLeaderboard(string leaderboardID, int score)
     {
         Social.ReportScore((long)score, leaderboardID, success => { });
     }

Then at the end of each game, when the game over menu appears, t$$anonymous$$s line is called w$$anonymous$$ch calls the above function in the Leaderboard class (I've blocked out the leader-board ID):

 leaderboard.AddScoreToLeaderboard("exampleID1234", runtime.GetComponent<ScoreTracker>().score);

I've done t$$anonymous$$s since the actual $$anonymous$$gh score is stored in Player Prefs w$$anonymous$$ch could be edited by knowledgeable players, so instead at the end of each run the current score stored in my ScoreTracker script is submitted. At t$$anonymous$$s point a player can use one revive though w$$anonymous$$ch just means at the end of that run and the game over screen appears again the line above is called once again, w$$anonymous$$ch should just update the score if $$anonymous$$gher regardless.

Is t$$anonymous$$s a bad way about going using the google play leader-board system and is there somet$$anonymous$$ng I'm doing wrong?

Any help would be greatly appreciated, thanks.