Full payment is done, possession letter is not signed as work is incomplete,but started living there

I booked a flat in a RERA registerd project in february 2018, completion date was 31st may, 2018. As 98% building work was done, builder was continuously asking us to take possession. As our loan EMI's started in March 2018 and the builder gave us the keys without signing any possession/allotment letter we started living the flat.But till today i.e., june 2019 amenities are not completed, electric meters are installed on 15 June 2019, muncipal corporation water supply is not started. 1)In this situation, can I file a complaint in RERA to get the compensation for delay in amenities and delayed possession and as I started living the flat after 3 months from the possession date and I have not signed on the allotment letter. I am not alone to do this, 5-6 flat holders are living in the building without signing the possession/allotment letter. 2) I have asked him many times to show the OC if he has received, but he has shown only partial completion letter. I a unable to know if he has the OC or not