Builder is not giving sale deed document

I purchased a flat in a new building in the year 2007. I didn't had any previous experience or knowledge of properties and its documents. I have shifted to a new apartment so I want to sale the flat I purchased in 2007. Last year one person was interested in purchasing the flat, everything was going well but the bank refused to offer the loan as I didn't had sale deed document. I am following-up with the builder for the sale deed document from last few years but he is not taking any serious steps to issue the sale deed document to all the residents of the building. His latest excuse is that he has given revised plan to the corporation and they are waiting for the approval. It's been more than a year for this excuse. The residents are not co-operative but still I managed to bring all of them together and issued a notice to the builder few months ago. We gave a written application with the signatures of all the residents for the sale deed document. The builder was not there to accept the letter, one of his staff member accepted the letter. He signed, stamped and gave one copy to us and kept one copy with him. The staff person said that sale deed issue is sorted and it will be executed within a week or two. Later when we went for the sale deed the same person straight away denied about the sale deed execution. I am fed up wasting my time for this. What action should I take so that I get the sale deed document? Looking forward to your suggestions.