Amendment in layout plan of building without intimation to society

I have purchased a flat in Thane municipal corporation region, in MAY 2016 , when RERA rules was not in fuction, after the implementation of RERA builder have handed over the possession in July 2018 and O.C. in Sep 2018, during the purchase of the Flat a small portion of our Buildings Stilt area on Ground floor is shown as HEALTH CENTER but at the time of society formation and handover which is done in JAN 2019 ,Builder have changed that HEALTH CENTER area in to 2 numbers of Professional Offices and said to Society members that he is going to sale those. he also a created a Garage type structure next to those office in stilt area of building with putting mechanical rolling shutters to it saying that those parking will be sold to office owners. he have not informed any of society members nor taken any consent of pre-booked flat owner before doing this. Now my Question is as per RERA act section 14 can builder change and execute such type of changes in already approved plans without notice or without consent of flat owners...? and if it is out of law or violation of ACT then what action we can take to file a case against the builder and what kind of action will be taken if we won this case against the Builder...?