I suggest you go to the Council and obtain the original plans for the block that were approved. The plans will show what was approved in terms of the construction etc. of that unit, including the habitable space and the balcony, as it was originally intended.
If the owner then altered the unit to enclose the balcony without Council approval then it won’t meet the requirements of the original approval, and on its face is illegal. In those circumstances a Council can issue an order for the owner to rectify/reinstate so it meets the original plans. Bear in mind that the building standards that apply to a balcony will differ in a number of respects from those that apply to a habitable space, in terms of waterproofing etc.
It is then up to the owner to deal with Council and put in an application for approval of any changes to the unit. From what you have said, it seems that the unit as it currently is does not meet Council requirements, and it would be up to the owner to do the work to bring it to any conditions the Council requires.
The configuration of the window actually sounds dangerous. In terms of the removal of the wall between the balcony and the living space, that may have been a load-bearing wall. If this is the case then the owner would have to obtain Council approval to remove it and ensure it was structurally sound.
Presuming the approved plans don’t match what is currently there, you can report it to Council and they can take enforcement action.