As for your talents, if you're struggling to keep track of all your cooldowns and buffs, then I think that you should think about using Incanter's Ward over Invocation. In a perfect world, I'm suggesting a DPS loss, but if you're having issues keeping track of Invocation, then IW is just one less thing to worry about.
You might also try out using Nether Tempest instead of Frost Bomb, for multiple reasons. It's better dps for anything short of AoEing, and your Light of the Cosmos trinket only procs from damage over time effects. As frost, without Nether Tempest or Living bomb, you have no damage over time effects, meaning that what should be a very useful trinket is only worth its haste value.
If those don't help, inspect the people beating you and make mental excuses based on being outgeared, fight mechanics, and per scenario class imbalances.
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