Maintenance dispute

Hello, we have purchased a flat in Bangalore in 2013, tht time they had mentioned that we have to pay 2 years advance maintenance of Rs. 33,444 (at the time of possession/ registration whichever is earlier). Then in Apr 2015 they told us to pay the maintenance amount and other charges to get possession before registration , so we paid the maintenance amount along with other charges. We got the possession letter (date not mentioned anywhere on the letter)alongwith the Bescom installation letter on the builder letterhead after we registered our flat in March 2016. Now the builder is asking us to pay the maintenance amount of the year 2017 also whereas we have already paid 2 years in advance but the builder is calculating those 2 years advance from April 2015 when they had told us to pay the maintenance, but 2 years have to start from the date of possession letter provided. And also the association has put us in defaulters list and shuting down our water and electricity. Please let us knw how to deal with this matter.