Are we liable to pay maintenance amount between possession and registration which is 10 years?

My grandfather was an old tenant of a building which went for redevelopment in 2010, during the period of construction my grandfather passed away and the 2 flats that we were supposed to be given in the new building were given in the name of my father and uncle. on completion of the building in 2013 only the possession letter for both flats was given to my father. After chasing the builder for the last 10 years who on some pretext or the other kept delaying the registration for reasons best known to him, we finally registered the property on `jan 19 2023 after being demanded a bribe to get things finally don which we agreed to as we just wanted the registration to be done, post which the builder told us he would courier the agreements to us. its approx 15-20 days now and on inquiring with the builder on the status of the agreements we have been asked to pay an amount of 2 lakhs as "maintenance charges" for the period of 2013-2017 which is from time of completion of the building to the handover to the society. we do not have the lumpsum to be paid overnight and the builder is now threatening to hold back the document till we pay the amount. We have regularly been paying the society the maintenance since the society came into effect. prior to this we have never heard of or were told absolutely anything about this amount by the builder. Are we liable to pay this maintenance amount considering the registration has been completed this year?