Supertech Ltd — default in payment of subvention emi, non-issuance of rental cheques

Address: New Delhi, Delhi, 110091

I bought a studio apartment in supertech upcountry, which was under subvention plan. The builder did not pay the emi last month, following which the bank invoked a cheque and withdrew whatever amount was there in my account. No fund in my account triggered a series of default by me paying other emis, thereby, reflecting badly on my credit score.
Also, at the time of booking the flat, i was promised rental cheques for 36 months, which the builder has not issued in last 15 months since i booked the flat. Each mail that i have written to the builder on the issue has remained unanswered. Don't know what to do