How can I get possession of my flat from builder

I have booked a LIG flat at Baruipur, 24 Pargana (S), in the year 2011, in my allotment letter mentioned possession will be given after 33 months. Now almost 50 months over, I have seen physically that my flat is not build till date, other flats in the complex are semi finished, its a joint venture of West Bengal Housing Board & Bengal Shrachi Housing Development Ltd. I have applied for a home loan to Axis Bank (approved project), & get the allotment letter in April'2015, it is valid for 6 month, so I have to take 1st disbursement within 6 month, but Builder is not giving me the demand letter for the installment, nor giving me reply of my emails. I actually want to know from builder, when can they will give the possession ? I am paying Rs.5000/- rent P.M. so I need possession immediately. But as per actual status I think they will take at least 2 years more to complete the construction ! Main thing they are not giving me the actual information, nor giving reply of my mails, Now kindly let me what can I do ?