Why do you say it’s common property?
Technically, you only own what’s inside the the external walls of your apartment, plus or minus a few specific exceptions. Your windows and balcony, if you have one, are common property. The concrete slab under your flooring is common property, as is the ceiling. Your front door and the closure mechanism attached to it are both common property.
Look at it this way, anything around or inside your unit that is shared by or might impact on a neighbour above, below or next to you, plus adjacent common property areas too, are all common property. You own the air inside the apartment and any non-load-bearing walls withing the area too.
You own and are responsible for a share in common property which is why you need to get on to your defects ASAP – because you will end up paying a share of the cost of fixing issues in other apartments if you don’t.
All of which leads me to beseech you to ask a professional for their advice because I am sensing you are way out of your depth here and that is being taken advantage of by your developer, builder and maybe even your building manager.