Well it has happened now and there is not much you can do about it.

That is the chance you take when you buy any sort of foodstuffs or plants from overseas.  Rules change, the inspecting officers change and maybe don't interpret the rules in the same way.

The letter you received from Customs should have told you why the item was impounded...they don't just grab it and tell you nothing.  You are usually given an option to contact someone if you feel the items were falsely impounded.