1) since you have proof of payment of advance amount of Rs 1 lakh and obtained receipt from builder you should call upon builder to enter into regd sale deed and deliver flat to you . you should mention that you are willing to make payment of balance amount as agreed .
2) you should move consumer forum against builder for deficiency in service and seek orders to direct builder to enter into regd sale deed and hand over possession of flat to you . also challenge mail sent by builder cancelling your booking of flat
3) also seek compensation from builder .
4) in the alternative you can seek refund of money paid with interest at 18%pa