Can you ask your migration agent for proof that they actually submitted your application to Australia House in May 2011. From the timeframes you have given it sounds suspiciously like they didn't receive it until January 2012 - the advice of a 6 month wait from that point sounds about right.
Could it be possible they failed to submit it in time or perhaps submitted it incorrectly the first time round?
I would have a fairly blunt conversation with your migration agent to find out exactly what's happened...
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