Builder demanding addtional amount

Hi, I had purchased flat in aug 2015 in Panvel- Navi Mumbai . it was registered around sept 2015 . As per the demand I had paid all 95% of flat value. Since builder had not mentioned any possession date in flat he delayed the project. Now the project is registered with rera and possession date was in first week of May 2018 which is already passed Builder had send me demand letter demanding below amount & mentioned planning to give possession soon in letter. 5% pending amount Cidco naina charges 165000 Society registration charges 40000 2 Year maintenance charges – 32000 In agreement he had only mentioned amount for flat. I had already paid him 95 % amount as per the agreement. All amount is paid through bank loan. I had proof. but he had mentioned in a clause in agreement that I need to pay additional amount for cidco Naina / Society charges / 2 year society maintaince charges .No amount is mentioned for that . He had send me 2 letter as a remainder to pay above dues before possision of flat. When I raised Maharera concellation request he send me email that as per the agreement I need to pay above due otherwise he will terminate the agreement as per the clause . It was normal email without any lawyer name so i didnot proceed with maharera concellation request & looking for legal advice Please advice