Possission of flat without registration

We are living in flat ( in one society at Noida) for which registration is still pending by builder, although builder has promised to carry out the same (either 3 months) after flat purchase. It was taken in the year 2021 ( stamp duty of 2.5 lakhs also paid) with complete payment to builder. All necessary papers incl CC of society was handed over to me however builder is delaying the registration and enjoying benefit of increased CAM, electricity and others for years and so.Although in recent times they cone out with hefty demand for flats registartion which is not at all justified ( as there were no dues for any of the flat owners in scociety) . In this circumstances, Society AOA has decided to take ownership/ handover of society from the builder to stop their unscrupulous demand ( year by year ). In this situation, I enquire the following from you as follows: 1) Whether Handover is justified at this stage ( where Only partial registration of Society' flats are in place) 2) If YES, who will pursue the flat registration process ( is it still builder or AOA)? 3) Is it OK for the flat owners to get their flats registered at so called HIGH demand from Builder ( before handover) or wait for right momenent in future ( Even society handover takes place). Rgds, SUM