I had GameCenter synced to the original account as well, but it didn't help or do anything.
GameCenter still has my score at 10,830,880 as of June 15, 2016, if I go into Settings -> Game Center.
However, the game itself says I am Bronze 3 and only 173,030.

Trying the restore purchases did not work either.
I had pretty much every single gun except the locked Prestige leaderboard ones, all of which were near fully upgraded if not fully upgraded.
I also had the Merrymaker which was highly upgraded or completed (can't remember which, too long ago).

Please help!