Ceiling water ingress and damage

my concrete ceiling has water damage and excess moisture in half of my apartment. We have just carried out major roofing work to replace the membrane and we have had to recall the trades in to redo the area due to a poor result and the top coat failing.

in the meantime I’ve had tenant move in to a perfect apartment. As mentioned they advise that there is excessive water marks advisable throughout half the ceiling, ceiling paint cracking, water dripping and mould appearing as a result of the moisture.  

they called a plumber in and used the contractor that did the original work and they say there is no leek and for the tenant to turn off the gas heater. The contractor will conduct a flood test. I’m really not happy with this proposed solution. The unit is huge with 9 foot ceilings. There is evidence of water ingress but they are not listening to me.  I want an engineer to be used to asses the issues who’s responsibility is this as I feel I’m being ignored. Thanks.