Why is it necessary to be still to hear the voice of God? The human is programmed to be busy. This is not part of your spiritual make-up, but a cultural learning. There are cultures that accept stillness as a rite, knowing that this will bring communion with the Self. Yours is a culture that values doing over being, accomplishing over inner knowing.
You can only know Truth by not accomplishing anything. Trying is counterproductive. Even in your attempts to reach a state of stillness you exert effort. Pay attention: Are you breathing with effort, or allowing the breaths to simply flow? Surrender and allow yourself to be breathed. Take time throughout your day to simply be and be breathed. Then and there in the silence and in perfect flow with the rhythm of the unforced breath will you hear the Voice. Allow it to be heard—not so still and small, but loud and clear once you have cleared the way through non-effort.