Builder exhausted maintenance funds asking additional money

Hello, I have taken possession of my flat in mid of 2015. At that time I have paid maintenance charges for next two years (till mid 2017). Recently all the flat owners received an email from builder telling us that all maintenance funds have been exhausted as of mid of last year and asking us to pay additional maintenance charges. He is also charging us Service Tax on top of maintenance charges. We have asked him to show where he has spent funds and he has sent us excel files showing where all the money went. Builder has not yet handed over the society to us. Question: 1.] Should we pay additional maintenance charges? We had no control over how builder has spent his money in the past. We all think builder ran out of funds due to lack of planning or some other reasons unknown to us. 2] In the event we decide to pay additional maintenance charges, should we even any service tax? 3] Should we need legal representation in this matter, what kind of lawyer we need real estate lawyer or some other specialty? Appreciate all the help you can offer.