Hi
If it is a recently constructed strata building this should be covered by the new building warranty insurance from the construction company.
The surface area between the upper & lower units are responsibility of the OC of the strata scheme. The strata manger agent, only acts under lawful direction from the OC executive and advise on some state strata regs.
There for with evidence you have and quote for repair arrange special meeting with the body corp members seeking the majority approval. Even though this may not been budgeted for from the previous AGM. The executive may attempt to claim this on the strata insurance. You have a valid claim form the strata scheme for repair of the damaged ceiling. Regardless of how the strata scheme pay for this repair. Instruct agent of there request.
If this fails, commence mediation with DFT, keep written records along with potos of damaged ceiling of all decisions with this matter.
Kind Regards,
Digby