Please help!

Hi There, I have bought a residential property in Pune in March 2018 and the only document I have is registered sale agreement and few other project related documents + society share holder certificate. Parties involved in the sale agreement are developer, land owner and buyer (me). I availed the home loan from LIC HFL and now trying to switch this loan to SBI.. however in the balance transfer process SBI is demanding registered sale deed between builder and land owner to have a proof that this particular property belongs the land owner quota from total developed units. Land owner has builder issued declaration deed mentioning the flat number but it is not registered. What can be done in this case? Builder is refusing to execute any further documents with me. Should I ask land owner to execute a registered sale deed between him and developer now? and once this deed is complete should i execute a confirmation deed between me and land owner? Note : the society is registered and in a process to get deemed conveyance without builder. Kindly help with your valuable advise!