Chances are the heat is escaping faster than you're putting it in. A candle actually produces a high enough temperature to melt gold, but it doesn't provide very much of that temperature. As soon as you get a couple of millimeters away from the hottest part of the flame, it gets too cool. A graphite mold will conduct heat away from itself very well, so you're not putting enough heat in to get the gold molten.
Imagine trying to water your lawn on a hot day. If you try with a tiny hose with a drinking straw on the end of the hose, the water will dry up almost as fast as you try to put it on. Your lawn will die. But if you use a larger hose and let it flow through a larger opening, like a large lawn sprinkler, you'll wet and saturate the ground and your lawn will survive.
It's the same when you try to melt gold. You have to put heat into the system faster than it's escaping to get it hot enough to melt the gold. I'm guessing that the heat is escaping faster than you're putting it in.
Try a melting dish that's well insulated and you should enjoy success.
Dave