No occupancy certificate.. permissive possesion

Dear Sir/Madam, Please help me with my query here. I bought an apartment from a builder in Gurgaon. As per agreement he needed to deliver in March 2014. The builder sent us a permissive occupancy letter and a bill to submit the remaining penning amount with them. When i checked the apartment it was in such shabby state, no human could have lived there. I refused to make the remaining payment that as per agreement had to be given when possession is given. Not only the apartment was in a bad shape, they started sending us bills for interest as well. Please help me understand can he charge me interest on pending payment when poses ion is not been given to me. He does not have the occupancy certificate and his lawyer has sent me a letter that they don't need an occupancy certificate to raise this bill or giving permissive possession. is it really true?? 1) can he offer me permissive possession of the apartment when apartment is not ready yet? 2) Can he charge me interest on pending payment when poses ion is been given to me (as per agreement signed, we needed to make this payment only on poses ion of the apartment) regards and thanks in advance..