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Excessive tax on new-build flat in France

I am a co-owner of a new-build flat. We received demands for excessive payments of taxe foncière despite the fact that the apartments are uninhabitable (certified by the police) and no completion certificates had been sent to the mairie. What are the rules relating to a first payment on a new property of this tax and what factors are taken into account in assessing the tax’s base level? M.S.