You might also try mentioning what Country you are in, as your problems depend greatly on that.
In the UK Neutral is connected to Earth at the sub-station, so it 'should' work regardless of the neutral connection been connected to either Neutral or Earth - but I would seriously suggest that it SHOULD be connected correctly.
'Generally' with three phase in the UK there should be very little current carried in the Neutral connection, as one of the main points of three phase is that the phase loads should be fairly well balanced, and only the small unbalance current flows down the Neutral wire. For this reason three phase often has three thick live wires, and a thinner neutral.
But it sounds like you need some competent rewiring?.