Poseesion certificate and maintenance

I bought my flat n haryana from builder and got it registered in October 2016.along with it paid one year advance maintenance charges to the maintenance agency made by builder for housing society. Though I paid the amount in full..I didn't take delivery of possession of flat as flat had many issues like broken ceiling ..etc..as per buyers agreement. Now buliders maintenance agency is asking for maintenance from October 2017 - till date. Maintenance agency states that since conveyance deed, undertaking n indemnity had possession clauses..n they were signed by me hence I am liable to pay maintenance ..whether physical possession of flat is taken or not..it doesn't matter. I keep writing to them that though they offered possession notice but I haven't been able to take possession ,as work under question was never completed n confirmed to me.Also no possession certificate ..with any documents regarding parking,keys of house being handed over to me .I have a letter stating that I have paid full amount along with advance maintenance for one year and also stating that I m not taking possession due to work not completed which is stamped and received by them in octobrr2016...Still they are raising demand for subsequent maintenance and also not providing me possession certificate, occupancy and completion certificate..Should I.move to RERA? What should I do?