Is builder eligible for 6 months grace period?

On April,2013 my agreement was done and I got possession on Feb,2016.As per MOM with builder I will be entitled to get compensation Rs 12000 as 3 months rent(Written Communication) from builder if they delayed the possession date which was mentioned on agreement(30 month).Later on builder changed their statement and said the compensation amount will be adjusted with maintenance amount which was supposed to paid by me(Rs 48,000) to builder and only those buyers will be eligible who got delayed possession as per agreement(No written communication).Two years back I got maintenance amount due reminder mail (After adjusting delayed compensation Rs 12000) with from builder side.I immediately paid that amount .Recently they stooped my housekeeping services (Picking up garbage) without any notification or communication and asking for the Rs 36000 more by saying they didn't calculate grace period previously now they are calculating grace period and asking full maintenance amount .Point to be mentioned here they never mentioned 6 month grace period in the agreement only mentioned "The promoter shall be entitled to reasonable extension of time giving delivery of flat on the aforesaid date,if the completion of the building is delayed on account of . 1. Non-availability of steel,cement,other building material, water or electricity supply.2. War,Civil commotion or act of God" .They are saying its mentioned in law. Now please help me and guide me what should I do? Thanks Regards Laltu Dey